Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Yuta Tsuji Last modified date:2022.04.14

Associate Professor / Faculty of Engineering Sciences


Papers
1. Wataru Hashimoto, Yuta Tsuji, Kazunari Yoshizawa, Optimization of Work Function via Bayesian Machine Learning Combined with First-Principles Calculation, Journal of Physical Chemistry C, 10.1021/acs.jpcc.0c01106, 124, 18, 9958-9970, 2020.05, Work function is one of the most fundamental and important physical quantities in surface science. Materials with either lower work function or higher work function would find various applications, such as electronic devices and high-performance catalysts. However, it would be challenging to find a material with the optimal work function exploiting the all-search or random approach, whether it is based on an experimental or theoretical method. In this paper, we use the Bayesian optimization (BO) approach, which is one of the most powerful machine-learning tools for optimization, in order to effectively explore a candidate material with a higher or lower work function value out of hundreds of thousands of materials registered in a material database. We introduce a quick measure of the work function based on the depth of the Fermi level calculated from the first-principles computation for the crystalline bulk structure of a material. We call this the approximate work function, treating it as the objective function of our BO scheme. Since we do not need any time-consuming surface calculation with the slab model for the evaluation of the approximate work function, a quick search of a material with the highest or the lowest work function is achieved. As input variables for our BO implementation, we employ some bulk-specific properties of materials, which can be fetched from the database. The demonstration of our BO-based exploration of the database shows that materials with both low and high limits of the approximate work function can be discovered more efficiently in BO than a random exploration. The top 10 lowest work function materials thus found are in line with our chemical intuition in that all of them include either alkali or alkaline earth metal. On the other hand, we found the top 10 highest work function materials with amazement because they also include either alkali or alkaline earth metal and a lanthanide element..
2. Theoretical Study on the Relation between the Frontier Orbital and the Conductance in Aromatic Single-Molecular Parallel Circuits.
3. Kazuki Okazawa, Yuta Tsuji, Kazunari Yoshizawa, Understanding Single-Molecule Parallel Circuits on the Basis of Frontier Orbital Theory, Journal of Physical Chemistry C, 10.1021/acs.jpcc.9b08595, 124, 5, 3322-3331, 2020.02, In electronic devices, as the number of paths connecting source and drain electrodes increases, the conductance of the device will also increase. However, this is not always the case on the nanoscale. According to the current superposition law at work in the macroscopic electrical circuits, doubling the number of paths should double the conductance, but when such paths are examined on the basis of the frontier orbital theory for nanoscale electrical circuits, more complex scenarios arise. When the number of paths in a molecule is doubled, the conductance may get more than doubled, remain unchanged, or even be reduced. We propose a classification of conducting systems falling into each of these scenarios with the help of aromaticity. The present work involves a theoretical study using the nonequilibrium Green's function that shows that these varying outcomes are closely related to the presence or absence of aromatic rings. This work serves to characterize molecular conductance characteristics based on frontier orbital theory, orbital interactions, and a local transmission concept. Some discrete mathematical aspects of the relationship between atom connectivity and electron conductivity are also described..
4. Yuta Tsuji, Mikiya Hori, Kazunari Yoshizawa, Theoretical Study on the Electronic Structure of Heavy Alkali-Metal Suboxides, Inorganic chemistry, 10.1021/acs.inorgchem.9b03046, 59, 2, 1340-1354, 2020.01, On the metal-rich side of the phase diagrams of the Rb-O, Cs-O, and Rb-Cs-O systems, one can find a variety of stoichiometries: for example, Rb9O2, Rb6O, Cs4O, Cs7O, Cs11O3, RbCs11O3, and Rb7Cs11O3. They may be termed heavy alkali-metal suboxides. The application of the standard electron-counting scheme to these compounds suggests the presence of surplus electrons. This motivated us to carry out a theoretical study using the first-principles density functional theory (DFT) method. The structures of these compounds are based on either a formally cationic Rb9O2 or Cs11O3 cluster. The analyses of the partial charge density just below the Fermi level and the electron localization function (ELF) have revealed that there exist surplus electrons in interstitial regions of all the investigated suboxides so that the excess positive charge of the cluster can be compensated. Density of states (DOS) calculations suggest that all of the compounds are metallic. Therefore, the suboxides listed above may be regarded as a new family of metallic electrides, where coreless electrons reside in interstitial spaces and provide a conduction channel. Except for the phases of Rb9O2 and Cs11O3, the suboxide structures include both the cationic clusters and alkali-metal matrix. Several charge analyses indicate that the interstitial surplus-electron density can be assigned to the alkali-metal atoms in the metal matrix, leading to the possibility of the presence of negatively charged alkali-metal atoms, namely Rb- (rubidide) and Cs- (caeside) ions, a.k.a. alkalides. In Rb6O, Rb-, Rb0, and Rb+ are found to coexist in the same crystal structure. Similarly, in Cs7O, one can find the three types of Cs atoms. However, in Cs4O, no Cs0 state is identified. In the Rb-Cs-O ternary suboxides, Rb takes a negatively charged anion state or neutral state, while all of the Cs atoms are found to be cationic because they get involved in the Cs11O3 cluster and all the Rb atoms exist in interstitial sites. Orbital interactions between the clusters are analyzed to understand how the condensation of the clusters into the solid happens and how the electride nature ensues. These clusters are found to have some superatomic character..
5. Yuta Tsuji, Ernesto Estrada, Influence of long-range interactions on quantum interference in molecular conduction. A tight-binding (Hückel) approach, Journal of Chemical Physics, 10.1063/1.5097330, 150, 20, 2019.05, When certain pairs of atoms in a π-conjugated molecule are connected with nanometer-scale source and drain electrodes, the remarkable quantum interference (QI) effect may arise. In this case, the electron transmission probability is significantly suppressed due to the QI effect. Tight-binding approaches, such as the Hückel molecular orbital (HMO) model, have revealed important features of this quantum phenomenon. However, important deviations from experiments and from more sophisticated calculations are known for a variety of cases. Here, we propose an extension of the HMO method to include non-nearest-neighbor interactions. Such long-range interactions (LRIs) are implemented in the HMO model in the form of a damping function that decays as the topological distance - the number of bonds separating two atoms - gets larger. The proposed model is further developed so that a geometric modification, i.e., the rotation around a single bond, can be taken into account. Our results show that LRI affects both the location of the antiresonance peak due to QI and the intensity of QI, even suppressing it in some cases. These results agree well with what was observed in a Density Functional based Tight-Binding (DFTB) study reported in the literature. These properties can be interpreted on the basis of a graph-theoretic path-counting model as well as the molecular orbital theory. In addition, the geometric LRI model is shown to reproduce the change of transmission as a function of rotation around the single bond separating two benzene rings in biphenyl, in agreement with what was observed in both experiment and DFTB calculation..
6. Junjing Gu, Wei Wu, Thijs Stuyver, David Danovich, Roald Hoffmann, Yuta Tsuji, Sason Shaik, Cross Conjugation in Polyenes and Related Hydrocarbons
What Can Be Learned from Valence Bond Theory about Single-Molecule Conductance?, Journal of the American Chemical Society, 10.1021/jacs.9b01420, 141, 14, 6030-6047, 2019.04, This study examined the nature of the electronic structure of representative cross-conjugated polyenes from a valence bond (VB) perspective. Our VBSCF calculations on a prototypical dendralene model reveal a remarkable inhibition of the delocalization compared to linear polyenes. Especially along the C-C backbone, the delocalization is virtually quenched so that these compounds can essentially be considered as sets of isolated butadiene units. In direct contrast to the dendralene chains, quinodimethane compounds exhibit an enhancement in their delocalization compared to linear polyenes. We demonstrate that this quenching/enhancement of the delocalization is inherently connected to the relative weights of specific types of long-bond VB structures. From our ab initio treatment, many localization/delocalization-related concepts and phenomena, central to both organic chemistry and single-molecule electronics, emerge. Not only do we find direct insight into the relation between topology and the occurrence of quantum interference (QI), but we also find a phenomenological justification of the recently proposed diradical character-based rule for the estimation of the magnitude of molecular conductance. Generally, our results can be conceptualized using the "arrow-pushing" concept, originating from resonance theory..
7. Junjing Gu, Wei Wu, Thijs Stuyver, David Danovich, Roald Hoffmann, Yuta Tsuji, Sason Shaik, Cross Conjugation in Polyenes and Related Hydrocarbons
What Can Be Learned from Valence Bond Theory about Single-Molecule Conductance?, Journal of the American Chemical Society, 10.1021/jacs.9b01420, 141, 14, 6030-6047, 2019.04, This study examined the nature of the electronic structure of representative cross-conjugated polyenes from a valence bond (VB) perspective. Our VBSCF calculations on a prototypical dendralene model reveal a remarkable inhibition of the delocalization compared to linear polyenes. Especially along the C-C backbone, the delocalization is virtually quenched so that these compounds can essentially be considered as sets of isolated butadiene units. In direct contrast to the dendralene chains, quinodimethane compounds exhibit an enhancement in their delocalization compared to linear polyenes. We demonstrate that this quenching/enhancement of the delocalization is inherently connected to the relative weights of specific types of long-bond VB structures. From our ab initio treatment, many localization/delocalization-related concepts and phenomena, central to both organic chemistry and single-molecule electronics, emerge. Not only do we find direct insight into the relation between topology and the occurrence of quantum interference (QI), but we also find a phenomenological justification of the recently proposed diradical character-based rule for the estimation of the magnitude of molecular conductance. Generally, our results can be conceptualized using the "arrow-pushing" concept, originating from resonance theory..
8. Rajib Kumar Singha, Yuta Tsuji, Muhammad Haris Mahyuddin, Kazunari Yoshizawa, Methane Activation at the Metal-Support Interface of Ni
4
-CeO
2
(111) Catalyst
A Theoretical Study, Journal of Physical Chemistry C, 10.1021/acs.jpcc.8b11973, 123, 15, 9788-9798, 2019.04, Methane activation is usually assumed to take place on top of metal surfaces or metal clusters. It can also occur at the metal-support interface in metal-supported catalysts with reducible oxides, such as CeO
2
. In the present work, we exploit density functional theory with an additional Hubbard-like parameter (DFT + U) to calculate the activation of methane at an O site interfacing a Ni
4
metal cluster on a support, CeO
2
(111) surface. Two reaction routes, namely, radical and nonradical routes, are taken into account. We show that the nonradical route is favored with an apparent activation energy of 18.1 kcal/mol, which is lower than that for the radical route by 15.0 kcal/mol. In the nonradical route, the formation of a four-centered transition-state structure is observed while a C-H bond of methane is being cleaved to form an OH moiety and a CH
3
fragment that is being bound to the interfacial Ni atom. It is also found that the interfacial O atoms are out of the CeO
2
surface plane with Ce-O bond distances being much longer than those in the crystalline bulk CeO
2
, which allows them to be easily reduced, and hence, the interfacial O atoms become more reactive toward methane, as compared to the surface O atoms. The interactions between Ni
4
cluster and the CeO
2
(111) surface result in the reduction of two Ce
4+
ions to Ce
3+
, improving the reducibility of the interfacial O atoms. This should be an important key to the facile methane activation..
9. Yuta Tsuji, Yasuhiro Kitamura, Masao Someya, Toshihiko Takano, Michio Yaginuma, Kohei Nakanishi, Kazunari Yoshizawa, Adhesion of epoxy resin with hexagonal boron nitride and graphite, ACS Omega, 10.1021/acsomega.9b00129, 4, 3, 4491-4504, 2019.03, Adhesion interaction of epoxy resin with the basal surfaces of h-BN and graphite is investigated with the first-principles density functional theory calculations in conjunction with the dispersion correction. The h-BN/epoxy and graphite/epoxy interfaces play an important role in producing nanocomposite materials with excellent thermal dissipation properties. The epoxy resin structure is simulated by using four kinds of fragmentary models. Their structures are optimized on the h-BN and graphite surfaces after an annealing simulation. The distance between the epoxy fragment and the surface is about 3 Å. At the interface between h-BN and epoxy resin, no H-bonding formation is observed, though one could expect that the active functional groups of epoxy resin, such as hydroxyl (OH) group, would be involved in a hydrogen-bonding interaction with nitrogen atoms of the h-BN surface. The adhesion energies for the two interfaces are calculated, showing that these two interfaces are characterized by almost the same strength of adhesion interaction. To obtain the adhesion force-separation curve for the two interfaces, the potential energy surface associated with the detachment of the epoxy fragment from the surface is calculated with the help of the nudged elastic band method and then the adhesion force is obtained by using either the Morse-potential approximation or the Hellmann-Feynman force calculation. The results from both methods agree with each other. The maximum adhesion force for the h-BN/epoxy interface is as high as that for the graphite/epoxy interface. To better understand this result, a force-decomposition analysis is carried out, and it has been disclosed that the adhesion forces working at both interfaces mainly come from the dispersion force. The trend of increase in the C
6
parameters used for the dispersion correction for the atoms included in the h-BN or graphite surface is in the order: N < C < B, which reasonably explains why the strengths of the dispersion forces operating at the two interfaces are similar. Also, the electron localization function analysis can explain why the h-BN surface cannot form an H bond with the hydroxyl group in epoxy resin..
10. Naoaki Tsurumi, Noriyuki Masago, Taiki Baba, Hiroyuki Murata, Yuta Tsuji, Kazunari Yoshizawa, A study of adhesion interface about die bonding structure with conductive silver paste, 2018 IEEE CPMT Symposium Japan, ICSJ 2018 2018 IEEE CPMT Symposium Japan, ICSJ 2018, 10.1109/ICSJ.2018.8602784, 45-48, 2019.01, In the electronic packages, gold surfaces are useful for stable connections. In this paper, adhesion interface for die bonding structure with conductive silver paste is investigated. The adhesive interface between gold surface and epoxy resin is investigated in two approaches. The first-principles calculations are employed to optimize the structure and calculate the theoretical bonding strength. The fragment model is constructed for bisphenol-A type epoxy resin and a curing agent which includes dicyandiamide. The results show that a cyano group included in the hardener greatly interacts with ideal gold surface, whereas a hydroxyl group seems not to interact with them regardless of high polarity. This interaction is likely to come from the π-back donation. The predicted bonding strength is as high as 1.15GPa. Next, the actual die pad surfaces prepared with plating gold are characterized to presume the substantial bonding structure by analytical method. Besides, measurements of adhesive strength have been performed by using small size lap shear tests under various temperatures. These results show that there are altered layers at the top of plating gold, which seems to affect the interaction mechanisms to hydrogen bond and make the adhesive strength lower..
11. Yuta Tsuji, Wataru Hashimoto, Kazunari Yoshizawa, Lithium-richest phase of lithium tetrelides Li17TT4 (TT = Si, Ge, Sn, and Pb) as an electride, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20190040, 92, 7, 1154-1169, 2019.01, The lithium-richest phase in the binary Li-Tt system (Tt = Si, Ge, Sn, and Pb) has a stoichiometry of Li17Tt4. In the beginning of this paper, the structural complexity of Li17Tt4 is gradually stripped away using the concept of the M26 cluster found in γ-brass structures and a Tt-centered polyhedral representation. By means of the first-principles electronic structure calculations, which are followed by the analyses of the electron localization function (ELF), Bader charges, and spin density, we observe non-nuclear maxima of the ELF, electron density, and spin density. Since the electron densities off the atoms are confined in crystalline voids, separated from each other, and behaving as an anion, Li17Tt4 can be identified as a potential zero-dimensional electride. This finding agrees with a simple Zintl picture, which suggests a valence electron count of [(Li+)17(Tt41)4¢e1]. Detailed analyses on the band structures, the projected density of states, and crystal orbitals at the ¥ point in the reciprocal space hint at the potential of forming a bond between the non-nuclear electron density and the neighboring atoms. Signatures of bonding and anti-bonding orbital interactions can be witnessed..
12. Thijs Stuyver, Tao Zeng, Yuta Tsuji, Paul Geerlings, Frank De Proft, Diradical Character as a Guiding Principle for the Insightful Design of Molecular Nanowires with an Increasing Conductance with Length, Nano Letters, 10.1021/acs.nanolett.8b03503, 18, 11, 7298-7304, 2018.11, In recent years, a considerable interest has grown in the design of molecular nanowires with an increasing conductance with length. The development of such nanowires is highly desirable because they could play an important role in future molecular-scale circuitry. Whereas the first experimental observation of this nonclassical behavior still has to be realized, a growing number of candidate wires have been proposed theoretically. In this Letter, we point out that all the wires with an anti-Ohmic increasing conductance with length proposed so far share a common characteristic: their diradical character increases with length. The conceptual connection between diradical character and conductance enables a systematic design of such anti-Ohmic wires and explains the difficulty in their syntheses. A strategy is proposed to balance the stability and conductance so that this nonclassical phenomenon can be observed..
13. Yuta Tsuji, Kazunari Yoshizawa, Effects of electron-phonon coupling on quantum interference in polyenes, Journal of Chemical Physics, 10.1063/1.5048955, 149, 13, 2018.10, It has been well accepted that when quantum interference (QI) occurs in a single molecular junction comprised of a π-conjugated molecule, the elastic π-electron transmission is blocked, while the elastic σ-electron transmission remains unchanged. When it comes to inelastic transport, in which passing electrons across the molecule trapped in between two metallic electrodes lose their energy through electron-phonon coupling, it is not necessarily obvious whether vibration affects the QI feature or not. In this paper, on the basis of a Hückel/tight-binding model, we address the inelastic transport through linear and cyclic polyenes which are conditioned to show QI. The zeroth-order Green's function approximated by the negative inverse of the adjacency matrix of a molecular graph is used in conjunction with the lowest order expansion of the self-consistent Born approximation. Owing to the simplification of the model, it just finds the limited applicability for the π-to-π scattering. Only topological aspects of dephasing are included. In such a theoretical construct, the alternant nature of the π-conjugated molecule is found helpful for classifying the dephasing patterns based on the parity of atomic sites. A rule is proposed, and it says that when both starred or both unstarred atoms are connected with the electrodes, QI always occurs, and atoms which belong to a different partite set from that of the atoms connected with the electrodes contribute to the inelastic π-to-π scattering. If QI occurs when a starred atom and an unstarred atom are connected with the electrodes, the contribution of the inelastic π-to-π scattering to the transport is expected to be unimportant..
14. Yuta Tsuji, Kazunari Yoshizawa, Adsorption and Activation of Methane on the (110) Surface of Rutile-type Metal Dioxides, Journal of Physical Chemistry C, 10.1021/acs.jpcc.8b03184, 122, 27, 15359-15381, 2018.07, Methane strongly adsorbs on the (110) surface of IrO
2
, a rutile-type metal dioxide. Its C-H bond is facilely dissociated even below room temperature, as predicted in a few theoretical works and actually observed in a recent experimental study. Thence, three questions are posed and answered in this paper: First, why does methane adsorb on the IrO
2
surface so strongly? Second, why is the surface so active for the C-H bond breaking reaction? Third, is there any other rutile-type metal dioxide that is more active than IrO
2
? A second-order perturbation theoretic approach is successfully applied to the analysis of the electronic structure of methane, which is found to be significantly distorted on the surface. Regarding the first point, it is clarified that an attractive orbital interaction between the surface Ir 5d
z2
orbital and the distorted methane's highest occupied molecular orbital leads to the strong adsorption. As for the second point, the bond strength between the surface metal atom and the CH
3
fragment generated after the C-H bond scission of methane is correlated well with the activation barrier. A substantial bonding interaction between CH
3
's nonbonding orbital and the dz
2
orbital hints at the strong Ir-CH
3
bond and hence high catalytic activity ensues. Last but not least, β-PtO
2
, a distorted rutile-type dioxide, is identified as a more active catalyst than IrO
2
. Here again, a perturbation theoretic line of explanation is found to be of tremendous help. This paper is at the intersection of theoretical, catalytic, inorganic, and physical chemistry. Also, it should serve as a model for the design and study of metal-oxide catalysts for the C-H bond activation of methane..
15. Yuta Tsuji, Ernesto Estrada, Ramis Movassagh, Roald Hoffmann, Quantum Interference, Graphs, Walks, and Polynomials, Chemical Reviews, 10.1021/acs.chemrev.7b00733, 118, 10, 4887-4911, 2018.05, In this paper, we explore quantum interference (QI) in molecular conductance from the point of view of graph theory and walks on lattices. By virtue of the Cayley-Hamilton theorem for characteristic polynomials and the Coulson-Rushbrooke pairing theorem for alternant hydrocarbons, it is possible to derive a finite series expansion of the Green's function for electron transmission in terms of the odd powers of the vertex adjacency matrix or Hückel matrix. This means that only odd-length walks on a molecular graph contribute to the conductivity through a molecule. Thus, if there are only even-length walks between two atoms, quantum interference is expected to occur in the electron transport between them. However, even if there are only odd-length walks between two atoms, a situation may come about where the contributions to the QI of some odd-length walks are canceled by others, leading to another class of quantum interference. For nonalternant hydrocarbons, the finite Green's function expansion may include both even and odd powers. Nevertheless, QI can in some circumstances come about for nonalternants from cancellation of odd- and even-length walk terms. We report some progress, but not a complete resolution, of the problem of understanding the coefficients in the expansion of the Green's function in a power series of the adjacency matrix, these coefficients being behind the cancellations that we have mentioned. Furthermore, we introduce a perturbation theory for transmission as well as some potentially useful infinite power series expansions of the Green's function..
16. Thijs Stuyver, Tao Zeng, Yuta Tsuji, Stijn Fias, Paul Geerlings, Frank De Proft, Captodative Substitution
A Strategy for Enhancing the Conductivity of Molecular Electronic Devices, Journal of Physical Chemistry C, 10.1021/acs.jpcc.7b10877, 122, 6, 3194-3200, 2018.02, We explore a new strategy to tune the conductivity of molecular electronic devices: captodative substitution. We demonstrate that a careful design of such substitution schemes on a benzene parental structure can enhance the conductivity by almost an order of magnitude under small bias. Once this new strategy has been established, we apply it to molecular wires and demonstrate that it enables the unprecedented anti-Ohmic design of wires whose conductivity increases with the length. Overall, the captodative substitution approach provides a very promising pathway toward full chemical control of the conductivity of molecules which opens up the possibility to design molecular switches with an improved on/off ratio among others..
17. Three Years at Cornell.
18. Yuta Tsuji, Thijs Stuyver, Suman Gunasekaran, Latha Venkataraman, The Influence of Linkers on Quantum Interference
A Linker Theorem, Journal of Physical Chemistry C, 10.1021/acs.jpcc.7b03493, 121, 27, 14451-14462, 2017.07, How heteroatomic substitutions affect electron transport through π-conjugated hydrocarbons has been the subject of some debate. In this paper we investigate the effect of heteroatomic linkers in a molecular junction on the electron-transmission spectrum, focusing on the occurrence of quantum interference (QI) close to the Fermi level, where conductivity can be significantly suppressed. We find that the substitution or addition of heteroatoms to a carbon skeleton at the contact positions does not change the main feature of QI due to the underlying carbon skeleton. QI in the overall system thus remains a robust feature. This empirical observation leads us to derive, in two mathematical ways, that these findings can be generalized. We note that addition or substitution of a carbon atom by a heteroatom at the contact positions will increase or decrease the number of electrons in the π-system, which will lead to a change in the alignment of the molecular orbitals of the isolated system relative to the electrode Fermi level. Both Hückel and density functional theory calculations on model systems probe the effect of this Fermi level change and confirm qualitatively the implications of the underlying mathematical proofs..
19. Junjing Gu, Wei Wu, David Danovich, Roald Hoffmann, Yuta Tsuji, Sason Shaik, Valence Bond Theory Reveals Hidden Delocalized Diradical Character of Polyenes, Journal of the American Chemical Society, 10.1021/jacs.7b04410, 139, 27, 9302-9316, 2017.07, The nature of the electronic-structure of polyenes, their delocalization features, and potential diradicaloid characters constitute a fundamental problem in chemistry. To address this problem, we used valence bond self-consistent field (VBSCF) calculations and modeling of polyenes, C2nH2n+2 (n = 2-10). The theoretical treatment shows that starting with n = 5, the polyene's wave function is mainly a shifting 1,4-diradicaloid, a character that increases as the chain length increases, while the contribution of the fundamental Lewis structure with alternating double and single bonds (1) decays quite fast and becomes minor relative to the diradicaloid pack. We show how, nevertheless, it is this wave function that predicts that polyenes will still exhibit alternating short/long CC bonds like the fundamental structure 1. Furthermore, despite the decay of the VB contribution of 1, it remains the single structure with the largest weight among all the individual structures. The mixing of all the 1,4-diradicaloid structures into 1 follows perturbation theory rules, with the result that the delocalization energy due to this mixing is additive and behaves as a linear function of the number of the double bonds, ΔEdel = -6.9 × n (kcal mol-1). The VB modeling shows that while the conjugation stabilizes structure 1, this stabilization energy is energetically overridden by the Pauli repulsion between two adjacent double bonds. Nevertheless, unsubstituted polyenes remain planar; this observation is addressed. Potential manifestations of the diradicaloid nature of polyenes are discussed, and it is concluded that the diradicaloid character is clearly not a well-defined physical property as in real diradicals. Thus, we went full circle to realize that our philosophical question may not be strictly resolved. The localized/delocalized properties of polyenes seem to define a "chemical duality principle". This duality of molecular wave functions is a ubiquitous beguiling phenomenon..
20. Yuta Tsuji, Kazunari Yoshizawa, Frontier Orbital Perspective for Quantum Interference in Alternant and Nonalternant Hydrocarbons, Journal of Physical Chemistry C, 10.1021/acs.jpcc.7b02274, 121, 17, 9621-9626, 2017.05, The wave-particle duality of electrons gives rise to quantum interference (QI) in single molecular devices. A significant challenge to be addressed in molecular electronics is to further develop chemical intuition to understand and predict QI features. In this study, an orbital rule is markedly ameliorated so that it can capture the manifestation of QI not only in alternant hydrocarbons but also in nonalternant ones. The orbital-based prediction about the occurrence of QI in a nonalternant hydrocarbon shows good agreement with experimental results. A simple perturbation theoretic line of reasoning suggests that frontier orbital phase and splitting play a pivotal role in QI phenomena..
21. Thijs Stuyver, Stijn Fias, Frank De Proft, Paul Geerlings, Yuta Tsuji, Roald Hoffmann, Enhancing the conductivity of molecular electronic devices, Journal of Chemical Physics, 10.1063/1.4972992, 146, 9, 2017.03, We show in this work that conjugated π-electron molecular chains can, in quite specific and understood circumstances, become more conductive the longer they get, in contradiction to what would be expected intuitively. The analysis, done in the framework of the source and sink potential method, and supported by detailed transmission calculations, begins by defining "relative transmission," an inherent measure of molecular conduction. This, in turn, for conjugated hydrocarbons, is related to a simple molecular orbital expression - the ratio of secular determinants of a molecule and one where the electrode contacts are deleted - and a valence bond idea, since these secular determinants can alternatively be expressed in terms of Kekulé structures. A plausible argument is given for relating the relative transmission to the weight of the diradical resonance structures in the resonance hybrid for a molecule. Chemical intuition can then be used to tune the conductivity of molecules by "pushing" them towards more or less diradical character. The relationship between relative transmission (which can rise indefinitely) and molecular transmission is carefully analyzed - there is a sweet spot here for engineering molecular devices. These new insights enable the rationalization of a wide variety of experimental and theoretical results for π-conjugated alternant hydrocarbons, especially the striking difference between extended oligophenylenes and related quinoid chains. In this context, oligo-p-phenylene macrocycles emerge as a potential molecular switch..
22. Ramis Movassagh, Gilbert Strang, Yuta Tsuji, Roald Hoffmann, The green's function for the huckel (tight binding) model, Journal of Mathematical Physics, 10.1063/1.4977080, 58, 3, 2017.03, Applications of the Huckel (tight binding) model are ubiquitous in quantum chemistry and solid state physics. The matrix representation of this model is isomorphic to an unoriented vertex adjacency matrix of a bipartite graph, which is also the Laplacian matrix plus twice the identity. In this paper, we analytically calculate the determinant and, when it exists, the inverse of this matrix in connection with the Green's function, G, of the N × N Huckel matrix. A corollary is a closed form expression for a Harmonic sum (Eq. (12)).We then extend the results to d-dimensional lattices, whose linear size is N. The existence of the inverse becomes a question of number theory. We prove a new theorem in number theory pertaining to vanishing sums of cosines and use it to prove that the inverse exists if and only if N + 1 and d are odd and d is smaller than the smallest divisor of N + 1. We corroborate our results by demonstrating the entry patterns of the Green's function and discuss applications related to transport and conductivity..
23. Fundamental and Applied Science, Academia and Industry, a Creative Tension in Today's Chemistry.
24. Catalyst Informatics on Methane Activation on Various Metal Alloys.
25. Yuta Tsuji, Prasad L.V.K. Dasari, S. F. Elatresh, Roald Hoffmann, N. W. Ashcroft, Structural Diversity and Electron Confinement in Li4N
Potential for 0-D, 2-D, and 3-D Electrides, Journal of the American Chemical Society, 10.1021/jacs.6b09067, 138, 42, 14108-14120, 2016.10, In pursuit of new lithium-rich phases and potential electrides within the Li-N phase diagram, we explore theoretically the ground-state structures and electronic properties of Li4N at P = 1 atm. Crystal structure exploration methods based on particle swarm optimization and evolutionary algorithms led to 25 distinct structures, including 23 dynamically stable structures, all quite close to each other in energy, but not in detailed structure. Several additional phases were obtained by following the imaginary phonon modes found in low-energy structures, as well as structures constructed to simulate segregation into Li and Li3N. The candidate Li4N structures all contain NLin polyhedra, with n = 6-9. They may be classified into three types, depending on their structural dimensionality: NLin extended polyhedral slabs joined by an elemental Li layer (type a), similar structures, but without the Li layer (type b), and three-dimensionally interconnected NLin polyhedra without any layering (type c). We investigate the electride nature of these structures using the electron localization function and partial charge density around the Fermi level. All of the structures can be characterized as electrides, but they differ in electronic dimensionality. Type-a and type-b structures may be classified as two-dimensional (2-D) electrides, while type-c structures emerge quite varied, as 0-D, 2-D, or 3-D. The calculated structural variety (as well as detailed models for amorphous and liquid Li4N) points to potential amorphous character and likely ionic conductivity in the material..
26. Yuta Tsuji, Roald Hoffmann, Helical Oligoenes
Conformations, Bond Alternation, and Competing Through-Bond and Through-Space Transmission, Chemistry - A European Journal, 10.1002/chem.201600042, 22, 14, 4878-4888, 2016.03, There is a consensus that long-range electron transfer/transport occurs by a through-bond rather than through-space mechanism. In helical all-Z, all-s-cis oligoenes, one can set up an interesting competition in the medium-separation regime between a closer (in distance) through-space path and a more distant through-bond one. Although such oligoene conformations/isomers are unstable (by around 4 kcal mol-1 per double bond relative to all-E, all-s-trans isomers), recent synthetic efforts on truncated helicenes and oligothiophenes have provided related molecules. On the way to transmission calculations with electrodes attached to the termini of helical oligoenes, we uncover an interesting conformational ambiguity in all-Z, all-s-cis oligoenes, the existence of a broad conformational minimum for helical compression, with hints of end-to-end frontier-orbital-caused stabilization. There is relationship between helical oligoene structures and the corresponding substructure of a helicene, but there are also significant differences in the number of olefin subunits per helix turn. In Hückel transport calculations, the role of TB or TS mechanisms is obscured to an extent by variations in bond alternation and dihedral angle along the oligomer chain. However, the operation of a dominant through bond mechanism emerges clearly in local transmission plots. In moving the electrodes to carbon position related by quantum interference, it is possible to uncover a through space mechanism..
27. Yuta Tsuji, Roald Hoffmann, Mikkel Strange, Gemma C. Solomon, Close relation between quantum interference in molecular conductance and diradical existence, Proceedings of the National Academy of Sciences of the United States of America, 10.1073/pnas.1518206113, 113, 4, E413-E419, 2016.01, An empirical observation of a relationship between a striking feature of electronic transmission through a π-system, destructive quantum interference (QI), on one hand, and the stability of diradicals on the other, leads to the proof of a general theorem that relates the two. Subject to a number of simplifying assumptions, in a π-electron system, QI occurs when electrodes are attached to those positions of an N-carbon atom N-electron closed-shell hydrocarbon where the matrix elements of the Green's function vanish. These zeros come in two types, which are called easy and hard. Suppose an N+2 atom, N+2 electron hydrocarbon is formed by substituting 2 CH2 groups at two atoms, where the electrodes were. Then, if a QI feature is associated with electrode attachment to the two atoms of the original N atom system, the resulting augmented N+2 molecule will be a diradical. If there is no QI feature, i.e., transmission of current is normal if electrodes are attached to the two atoms, the resulting hydrocarbon will not be a diradical but will have a classical closed-shell electronic structure. Moreover, where a diradical exists, the easy zero is associated with a nondisjoint diradical, and the hard zero is associated with a disjoint one. A related theorem is proven for deletion of two sites from a hydrocarbon..
28. Yuta Tsuji, Roald Hoffmann, Joel S. Miller, Revisiting Ir(CO)3Cl, Polyhedron, 10.1016/j.poly.2015.09.050, 103, 141-149, 2016.01, We return to an old puzzle - the short metal-metal separation and electrical conductivity of the apparently unoxidized one-dimensionally stacked structure of a d8 Ir(I) complex, Ir(CO)3Cl. One would expect neither a short Ir-Ir distance of 2.84 Å, nor metallicity in an unoxidized stacked square-planar d8 array. We build up dimer, trimer, one-dimensional polymer and model 3-dimensional structures, in both molecular and extended structure plane wave calculations. The short Ir-Ir separation in the polymer, with a substantial contribution of 6pz-5dz2 bonding to it, is obtained without any oxidation. There is computational evidence for an important level crossing in the polymer. The metallicity remains unexplained, but likely arises from partial oxidation. And that remains an outstanding experimental issue..
29. Yuta Tsuji, Ramis Movassagh, Supriyo Datta, Roald Hoffmann, Exponential Attenuation of Through-Bond Transmission in a Polyene
Theory and Potential Realizations, ACS Nano, 10.1021/acsnano.5b04615, 9, 11, 11109-11120, 2015.11, An exponential falloff with separation of electron transfer and transport through molecular wires is observed and has attracted theoretical attention. In this study, the attenuation of transmission in linear and cyclic polyenes is related to bond alternation. The explicit form of the zeroth Green's function in a Hückel model for bond-alternated polyenes leads to an analytical expression of the conductance decay factor β. The β values calculated from our model (βCN values, per repeat unit of double and single bond) range from 0.28 to 0.37, based on carotenoid crystal structures. These theoretical β values are slightly smaller than experimental values. The difference can be assigned to the effect of anchoring groups, which are not included in our model. A local transmission analysis for cyclic polyenes, and for [14]annulene in particular, shows that bond alternation affects dramatically not only the falloff behavior but also the choice of a transmission pathway by electrons. Transmission follows a well-demarcated system of π bonds, even when there is a shorter-distance path with roughly the same kind of electronic matter intervening..
30. Yuta Tsuji, Roald Hoffmann, Ramis Movassagh, Supriyo Datta, Quantum interference in polyenes, Journal of Chemical Physics, 10.1063/1.4903043, 141, 22, 2014.12, The explicit form of the zeroth Green's function in the Hückel model, approximated by the negative of the inverse of the Hückel matrix, has direct quantum interference consequences for molecular conductance. We derive a set of rules for transmission between two electrodes attached to a polyene, when the molecule is extended by an even number of carbons at either end (transmission unchanged) or by an odd number of carbons at both ends (transmission turned on or annihilated). These prescriptions for the occurrence of quantum interference lead to an unexpected consequence for switches which realize such extension through electrocyclic reactions: for some specific attachment modes the chemically closed ring will be the ON position of the switch. Normally the signs of the entries of the Green's function matrix are assumed to have no physical significance; however, we show that the signs may have observable consequences. In particular, in the case of multiple probe attachments - if coherence in probe connections can be arranged - in some cases new destructive interference results, while in others one may have constructive interference. One such case may already exist in the literature..
31. Yuta Tsuji, Roald Hoffmann, Frontier orbital control of molecular conductance and its switching, Angewandte Chemie - International Edition, 10.1002/anie.201311134, 53, 16, 4093-4097, 2014.04, For transmission of electrons through a π system, when the Landauer theory of molecular conductance is viewed from a molecular orbital (MO) perspective, there obtains a simple perturbation theoretic dependence, due to Yoshizawa and Tada, on a) the product of the orbital coefficients at the sites of electrode attachment, and b) the MO energies. The frontier orbitals consistently and simply indicate high or low transmission, even if other orbitals may contribute. This formalism, with its consequent reinforcement and/or interference of conductance, accounts for the (previously explained) difference in direct vs. cross conjugated transmission across an ethylene, as well as the comparative ON/OFF ratios in the experimentally investigated dimethyldihydropyrene and dithienylethene-type single-molecule switches. A strong dependence of the conductance on the site of attachment of the electrodes in a π system is an immediate extrapolation; the theory then predicts that for some specified sites the switching behavior will be inverted; i.e. the "open" molecular form of the switch will be more conductive. The phase and amplitude of the frontier molecular orbitals at the sites that are connected to electrodes play an essential role in determining transmission of electrons through a π system. When applied to two diarylethene switches, theory then predicts that for some specified sites the switching behavior will be inverted; that is, the "open" molecular form of the switch will be more conductive..
32. Takayuki Semoto, Yuta Tsuji, Hiromasa Tanaka, Kazunari Yoshizawa, Role of edge oxygen atoms on the adhesive interaction between carbon fiber and epoxy resin, Journal of Physical Chemistry C, 10.1021/jp407835d, 117, 47, 24830-24835, 2013.11, A mechanism of the adhesion between carbon fiber and epoxy resin is studied by using density functional theory (DFT) calculations. Surface structures of carbon fiber were modeled by the armchair-edge structure of graphite functionalized with OH and COOH groups. DFT calculations were performed to construct two realistic models of adhesion interface consisting of the functionalized carbon surface and a fragment of epoxy resin. Adhesive properties of the model interfaces were evaluated based on the binding energy (E b) between the carbon surface and the resin as well as the maximum adhesive force (Fmax) acting at the interface. Calculated values of Eb are 13.8 kcal/mol for the OH-functionalized surface and 19.1 kcal/mol for the COOH-functionalized surface. The binding energy per hydrogen bond is calculated to be 6.9 kcal/mol (OH model; two H-bonds) and 6.3 kcal/mol (COOH model; three H-bonds), both of which are virtually similar and reasonable for the bond energy of a typical OH···O hydrogen bond. Analysis of adhesive force-displacement curves derived from energy-displacement plots revealed that Fmax is 0.52 nN for the OH model and 0.70 nN for the COOH model. Calculated adhesive properties are in good agreement with those previously reported for the interface between an aluminum oxide surface and an epoxy resin [J. Phys. Chem. C 2011, 115, 11701], strongly suggesting that hydrogen bonds between the oxygen-containing functional groups play a crucial role in the adhesive interaction in the carbon fiber/epoxy resin system..
33. Yuta Tsuji, Takayuki Semoto, Kazunari Yoshizawa, A bipodal dicyano anchor unit for single-molecule spintronic devices, ChemPhysChem, 10.1002/cphc.201300136, 14, 11, 2470-2475, 2013.08, The conductance through single 7,7,8,8-tetracyanoquinodimethane (TCNQ) connected to gold electrodes is studied with the nonequilibrium Green's function method combined with density functional theory. The aim of the study is to derive the effect of a dicyano anchor group, =C(CN)2, on energy level alignment between the electrode Fermi level and a molecular energy level. The strong electron-withdrawing nature of the dicyano anchor group lowers the LUMO level of TCNQ, resulting in an extremely small energy barrier for electron injection. At zero bias, electron transfer from electrodes easily occurs and, as a consequence, the anion radical state of TCNQ with a magnetic moment is formed. The unpaired electron in the TCNQ anion radical causes an exchange splitting between the spin-α and spin-β transmission spectra, allowing the single TCNQ junction to act as a spin-filtering device..
34. Yuta Tsuji, Junya Koga, Kazunari Yoshizawa, Asymmetric diarylethene as a dual-functional device combining switch and diode, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20130089, 86, 8, 947-954, 2013.08, Diarylethenes are photosensitive φ-conjugated molecules, being of great promise in potential applications to various molecular devices. Although the switching properties of diarylethenes have been widely investigated experimentally and theoretically, little is known about their rectifying diode-like behavior. In this study, electron-transport properties of asymmetric diarylethenes incorporating two different heterocyclic five-membered rings with opposite electronic demands are investigated with the nonequilibrium Green function combined with density functional theory. The aim of this study is to derive the effect of the heteroatomic defects on not only switching but also rectifying characteristics of the asymmetric diarylethenes. Obtained results show that a silicon atom involved in the diarylethenes plays an important role in the current rectifying as well as switching performance. It is found that maximum rectification ratios of the asymmetric diarylethenes increase linearly with an increase in electronegativity difference between the asymmetrically arranged heteroatoms. The silicon- and oxygen-containing asymmetric diarylethene is suggested to be a good potential candidate for a novel molecular electronic device combining a switch and a diode..
35. Yuta Tsuji, Kazunari Yoshizawa, Current rectification through π-π Stacking in multilayered donor-acceptor cyclophanes, Journal of Physical Chemistry C, 10.1021/jp308849t, 116, 50, 26625-26635, 2012.12, Extended π-stacked molecules have attracted much attention since they play an essential role in both electronic devices and biological systems. In this article electron transport properties of a series of multilayered cyclophanes with the hydroquinone donor and quinone acceptor units in the external positions are theoretically studied with applications to molecular rectifiers in mind. Calculations of electron transport through the π-π stacked structures in the multilayered cyclophanes are performed by using nonequilibrium Green's function method combined with density functional theory. Calculated transmission spectra show that the conductance decreases exponentially with the length of the molecule with a decay factor of 0.75 Å-1, which lies for the values between π-conjugated molecules and σ-bonded molecules. Applied bias calculations provide current-voltage curves, which exhibit good rectifying behavior. The rectification mechanism in the coherent transport regime is qualitatively explained by the response of the frontier orbital energy levels, especially LUMO levels, to the applied bias, where the rectifying direction is expected to be opposite to the Aviram-Ratner model. The maximum value of rectification ratio increases with an increase in the number of stacking layers due to the effective separation of the donor and acceptor parts, where effects from the opposite electrodes to the donor and acceptor are negligible. Multilayered donor-acceptor cyclophanes are suitable materials for investigating the relationship among electron transport properties, rectification properties, and molecular length (separation between the donor and acceptor parts)..
36. Junya Koga, Yuta Tsuji, Kazunari Yoshizawa, Orbital control of single-molecule conductance perturbed by π-accepting anchor groups
Cyanide and isocyanide, Journal of Physical Chemistry C, 10.1021/jp3068156, 116, 38, 20607-20616, 2012.09, Electron transport properties through benzene molecules disubstituted with π-accepting cyanide and isocyanide anchor groups at their para and meta positions are investigated on the basis of a qualitative orbital analysis at the Hückel molecular orbital level of theory. The applicability of a previously derived orbital symmetry rule for electron transport is extended to the systems perturbed by the π-accepting anchor groups, where the HOMO-LUMO symmetry in the molecular orbital energies relative to the Fermi level is removed. The conservation of the HOMO-LUMO symmetry in the spatial distribution of the molecular orbitals between the unperturbed benzene molecule and the perturbed molecules with the anchor groups rationalizes symmetry-allowed electron transport through the para isomers. On the other hand, destructive interferences between the nearly 2-fold degenerate frontier orbitals constructed from the 2-fold degenerate orbitals of the unperturbed benzene molecule and the anchor groups lead to symmetry-forbidden electron transport through the meta isomers. The qualitative orbital thinking is supported by more quantitative density functional theory (DFT) calculations combined with the nonequilibrium Green's function (NEGF) method. The orbital analysis is a powerful tool for the understanding and rational design of molecular devices composed of π-conjugated hydrocarbons and those perturbed by the π-accepting anchor groups..
37. Aleksandar Tsekov Staykov, Xinqian Li, Yuta Tsuji, Kazunari Yoshizawa, Current rectification in nitrogen- and boron-doped nanographenes and cyclophanes, Journal of Physical Chemistry C, 10.1021/jp303843k, 116, 34, 18451-18459, 2012.08, Electron transport properties of boron- and nitrogen-doped polycyclic aromatic hydrocarbons and cyclophanes are investigated with the nonequilibrium Greens function method and compared to transport properties of the unsubstituted species. The aim of the study is to derive the effect of the heteroatomic defects on the conductance of nanographenes and to propose new effective ways for current control and design of carbon devices. Of special interest are the electrical current rectifying properties of asymmetrically doped nanographenes and cyclophanes, as well as the rectification mechanism. The mechanisms of donor-π bridge-acceptor and donor-σ bridge-acceptor rectification are used to explain the diode-like properties of asymmetrically doped nanographenes and cyclophanes. The electron-rich nitrogen and electron-poor boron heteroatoms introduce conductance channels within the highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of the hydrocarbons and cyclophanes and significantly enhance the conductance. The combination of nitrogen and boron impurities in one polycyclic aromatic hydrocarbon leads to asymmetrical I/V curves. The rectification is further enhanced in the cyclophanes where the boron impurities are located in one of the layers and the nitrogen impurities in the other. Owing to the efficient separation of the donor and acceptor parts, a higher rectification ratio is estimated. The rectifying properties of the asymmetrically doped carbon materials are derived from the nonequilibrium Greens function theory. The main reason for the rectification is found to be the interaction of the external electric field induced between the electrodes with the molecular orbitals of the asymmetrically doped hydrocarbons..
38. Yuta Tsuji, Aleksandar Tsekov Staykov, Kazunari Yoshizawa, Orbital determining spintronic properties of a π-conjugated system, Journal of Physical Chemistry C, 10.1021/jp305448q, 116, 30, 16325-16332, 2012.08, Spintronic properties of cyclobutadiene (CBD) systems are investigated based on a qualitative frontier orbital analysis. CBD undergoes a Jahn-Teller distortion from the square triplet state to the rectangular singlet state. According to the qualitative Hückel molecular orbital analysis, the electron transport through the square triplet state is symmetry allowed, whereas that through the rectangular singlet state is symmetry forbidden. The magnetic triplet state is a possible coexisting system of conductivity and magnetism. Sophisticated first-principles quantum chemical calculations are performed by using a realistic molecular junction model. Obtained results are in good agreement with the prediction based on the qualitative orbital analysis. Interesting spin filtering properties are found in the square-shaped CBD system. The high- and low-spin states of the square-shaped CBD system produce the spin-α and spin-β polarized conductance, respectively. The qualitative orbital analysis is useful as a guiding principle for designing molecular spintronics..
39. Takayuki Semoto, Yuta Tsuji, Kazunari Yoshizawa, Molecular understanding of the adhesive force between a metal oxide surface and an epoxy resin
Effects of surface water, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20120028, 85, 6, 672-678, 2012.06, A mechanism of the adhesion interaction between an aluminum oxide surface and an epoxy resin is investigated by using density-functional-theory (DFT) calculations. To understand effects of adsorbed water molecules on the adhesion interaction, hydroxylated aluminum oxide surfaces with adsorbed water molecules are prepared. Geometry optimization is performed for a model of adhesiveadherend complex, which is comprised of a fragment of epoxy resin and a wateradsorbed aluminum oxide surface. DFT calculations demonstrate that hydroxy groups and ether groups of epoxy resin can interact with the adherend surface via a hydrogen-bond network of adsorbed water molecules, which leads to a critical factor in the adhesion interaction. Plots of energy versus vertical distance of the resin from the surface are nicely approximated by the Morse potential. The force required for detachment of the resin from the surface can be estimated from the maximum value of the forcedistance curve, which is obtained from the derivative of the potential energy curve. Obtained results demonstrate that the hydrogen-bond network via adsorbed water molecules significantly affects the adhesion mechanism. The adsorbed water molecules provide a long-distance adhesion interaction but exert little influence over the maximum value of the adhesion force..
40. Molecular Theory of the Adhesion between Metal and Resin.
41. Yuta Tsuji, Aleksandar Tsekov Staykov, Kazunari Yoshizawa, Molecular rectifier based on π-π Stacked charge transfer complex, Journal of Physical Chemistry C, 10.1021/jp209547a, 116, 3, 2575-2580, 2012.01, Electron transport through π-π stacked materials has been studied theoretically and experimentally so far with versatile applications in mind. In this paper a novel π-π stacked molecular rectifier is proposed. Electron transport properties through cyclophane-type quinhydrone are investigated by using nonequilibrium Green's function method combined with density functional theory. The investigated molecule has a quinhydrone structure comprised of π-π stacked donor (hydroquinone) and acceptor (benzoquinone) pair due to the in-phase orbital interaction between the HOMO of hydroquinone and the LUMO of benzoquinone. A computed current-voltage curve shows rectifying behavior in the direction perpendicular to the ring plane. The maximum value of rectification ratio of 2.37 is obtained at 0.8 V. In this system the LUMO level plays a key role, and asymmetrical evolution of the LUMO level for positive and negative biases leads to the rectifying behavior. The present study is a basic step for further functionalization of a molecular rectifier based on transannular electron transport. The understanding of insight into the electron transport through a π-π stacked system will provide motivation for design of future molecular devices..
42. Molecular Theory of the Adhesion between Metal and Resin.
43. Masateru Taniguchi, Makusu Tsutsui, Ryoji Mogi, Tadashi Sugawara, Yuta Tsuji, Kazunari Yoshizawa, Tomoji Kawai, Dependence of single-molecule conductance on molecule junction symmetry, Journal of the American Chemical Society, 10.1021/ja2033926, 133, 30, 11426-11429, 2011.08, The symmetry of a molecule junction has been shown to play a significant role in determining the conductance of the molecule, but the details of how conductance changes with symmetry have heretofore been unknown. Herein, we investigate a naphthalenedithiol single-molecule system in which sulfur atoms from the molecule are anchored to two facing gold electrodes. In the studied system, the highest single-molecule conductance, for a molecule junction of 1,4-symmetry, is 110 times larger than the lowest single-molecule conductance, for a molecule junction of 2,7-symmetry. We demonstrate clearly that the measured dependence of molecule junction symmetry for single-molecule junctions agrees with theoretical predictions..
44. Takayuki Semoto, Yuta Tsuji, Kazunari Yoshizawa, Molecular understanding of the adhesive force between a metal oxide surface and an epoxy resin, Journal of Physical Chemistry C, 10.1021/jp202785b, 115, 23, 11701-11708, 2011.06, A mechanism of the adhesion between an aluminum oxide surface and an epoxy resin is investigated by using density functional theory (DFT) calculations. Force field simulations are carried out for a better understanding of the dynamic behavior of the resin on the surface and for constructing models for DFT calculations. Stable structures of a resinsurface complex, adhesion energies, and details about interaction sites are obtained from geometry optimizations for some models based on DFT calculations with a plane-wave basis set and periodic boundary conditions. DFT calculations reveal that hydroxyl groups of the epoxy resin interact with the surface of aluminum oxide to form hydrogen bonds, which work as a main force for the adhesion. Plots of energy versus vertical distance of the resin from the surface are nicely approximated by the Morse potential. The force required for detachment of the resin from the surface can be estimated from the maximum value of the force-distance curve, which is obtained from the derivative of the potential energy curve. Obtained results demonstrate that hydrogen bonds play a central role for the adhesion between an aluminum oxide surface and an epoxy resin..
45. Yuta Tsuji, Aleksandar Tsekov Staykov, Kazunari Yoshizawa, Orbital views of molecular conductance perturbed by anchor units, Journal of the American Chemical Society, 10.1021/ja111021e, 133, 15, 5955-5965, 2011.04, Site-specific electron transport phenomena through benzene and benzenedithiol derivatives are discussed on the basis of a qualitative Hückel molecular orbital analysis for better understanding of the effect of anchoring sulfur atoms. A recent work for the orbital control of electron transport through aromatic hydrocarbons provided an important concept for the design of high-conductance connections of a molecule with anchoring atoms. In this work the origin of the frontier orbitals of benzenedithiol derivatives, the effect of the sulfur atoms on the orbitals and on the electron transport properties, and the applicability of the theoretical concept on aromatic hydrocarbons with the anchoring units are studied. The results demonstrate that the orbital view predictions are applicable to molecules perturbed by the anchoring units. The electron transport properties of benzene are found to be qualitatively consistent with those of benzenedithiol with respect to the site dependence. To verify the result of the Hückel molecular orbital calculations, fragment molecular orbital analyses with the extended Hückel molecular orbital theory and electron transport calculations with density functional theory are performed. Calculated results are in good agreement with the orbital interaction analysis. The phase, amplitude, and spatial distribution of the frontier orbitals play an essential role in the design of the electron transport properties through aromatic hydrocarbons..
46. Aleksandar Tsekov Staykov, Yuta Tsuji, Kazunari Yoshizawa, Conductance through short DNA molecules, Journal of Physical Chemistry C, 10.1021/jp110803a, 115, 8, 3481-3490, 2011.03, The conductance through short DNA molecules connected to gold electrodes is studied with density functional theory and nonequilibrium Green's function method combined with density functional theory. The anchoring of the molecules to the electrodes is investigated, and in addition to the covalent S-Au bond, weak interactions between the aromatic heterocyclic bases and the electrodes are found. These weak interactions are important for the electron transport through DNA molecules. A tunneling mechanism is suggested, and the conductive properties of the nucleotides in a metal-molecule-metal junction are compared. Different four-nucleotide DNA sequences are investigated. A significant value for the current, 20 pA, is calculated for 1.5 V applied bias for a DNA sequence consisting of guanine and cytosine nucleotides. It is shown that adenine-thymine nucleotide pairs introduce potential barriers for the electron transport and therefore significantly decline the conductance. The obtained results are compared with recent experimental observations (Nanotechnology2009, 20, 115502) and confirm the possibility for electron transport through DNA molecules as well as provide an explanation for the reduced conductance through DNA sequences, which contain adenine-thymine nucleotide pairs. The results are compared with a previous theoretical study, performed with the extended Hückel method (ChemPhysChem2003, 4, 1256), which reports low conductance for DNA molecules. The difference in the conclusions is due to the applied bias self-consistent field calculations used in the recent study, which take into account the changes of the transmission probabilities with the bias..
47. Aiko Fukazawa, Manabu Kiguchi, Satoshi Tange, Yasunori Ichihashi, Qiang Zhao, Takuya Takahashi, Tatsuya Konishi, Kei Murakoshi, Yuta Tsuji, Aleksandar Tsekov Staykov, Kazunari Yoshizawa, Shigehiro Yamaguchi, Phosphine sulfides as an anchor unit for single molecule junctions, Chemistry Letters, 10.1246/cl.2011.174, 40, 2, 174-176, 2011, Phenylene and biphenyl compounds with dibenzophosphole sulfide (DBPS) as an anchoring group for single molecule junctions were synthesized. The conductance measurements revealed that the phosphine sulfide indeed acts as an anchoring group for Au electrodes. Theoretical calculations including metal electrodes demonstrated that the LUMO level of the DBPS-terminated biphenyl is close to the Au Fermi level, leading to the electron conduction of the AumoleculeAu junction based on the resonance-tunneling mechanism..
48. Yuta Tsuji, Aleksandar Tsekov Staykov, Kazunari Yoshizawa, Orbital view concept applied on photoswitching systems, Thin Solid Films, 10.1016/j.tsf.2009.07.037, 518, 2, 444-447, 2009.11, Diarylethenes are a class of photochromic molecules whose conductance switches with their photoisomerization. We have investigated the conductance of diarylethenes using non-equilibrium Green's function method combined with Hückel method (NEGF-HMO) and density functional theory (NEGF-DFT). In this study we have found that the qualitative predictions based on frontier orbital analysis are consistent with the DFT calculations and can be used for prediction of the electron transport properties of molecular devices..
49. Yuta Tsuji, Aleksandar Tsekov Staykov, Kazunari Yoshizawa, Orbital control of the conductance photoswitching in diarylethene, Journal of Physical Chemistry C, 10.1021/jp905663r, 113, 52, 21477-21483, 2009, Diarylethenes are photosensitive π-conjugated molecules whose application to various molecular devices is expected. The molecular and electronic structures of diarylethenes are switchable upon photoirradiation with their reversible structural isomerization. Site-specific electron transport phenomena through a diarylethene molecule, 1,2-di(2-methyl-1-naphthyl) perfluorocyclopentene, are studied by using the nonequilibrium Green's function method combined with the Hückel molecular orbital method (NEGF-HMO) and density functional theory (NEGF-DFT). On the basis of the orbital symmetry rule, the conductance of the diarylethene is predicted to be efficiently switchable when the C3 and C10 atoms are appropriately connected with electrodes. Transmission spectra, spatial distribution of the MPSH (molecular projected self-consistent Hamiltonian) states, and I-V curves are obtained from DFT calculations. These results obtained from the higher-level DFT calculations are consistent with the prediction based on the qualitative frontier orbital analysis at the HMO level of theory. The computed current for the closed-ring form of the 3-10 connection is about 3 orders of magnitude high compared with those for other connections. The phase, amplitude, and spatial distribution of the frontier orbitals play an essential role in designing the electron transport properties through the photoswitching system..
50. Phosphine Sulfide As an Anchor Unit for Metal-Molecule Junction.