Characterization of changes in the electronic structure of platinum sub-nanoclusters supported on graphene induced by oxygen adsorption.

As the sizes of noble metal catalysts, such as platinum, have been successfully minimized, fundamental insights into the electronic properties of metal sub-nanoclusters are increasingly sought for optimizing their catalytic performance. However, it is difficult to rationalize the catalytic activities of metal sub-nanoclusters owing to their more complex electronic structure compared with those of small molecules and bulky solids. In this study, the adsorption of molecular oxygen on a Pt13 sub-nanocluster supported on a graphene layer was analyzed using density functional theory. Unlike bulk Pt, the Pt13 sub-nanocluster has multiple adsorption sites, and the adsorption energy depends strongly on the type of adsorption site. The O2 adsorption energy does not correlate with the transferred charge between O2 and the Pt13 moiety; therefore, to elucidate the differences in the adsorption sites, we propose an original approach for analyzing the electronic structure change in metal sub-nanoclusters caused by molecular adsorption. Our analysis of the integrated local density of state (LDOS) revealed that O2 adsorption on the Pt13 sub-nanocluster has a distinct feature, different from that on a smaller Pt2 cluster or rather a larger Pt slab. The change in the electronic structure of the Pt13 moiety was primarily observed near the Fermi level, different from that of the Pt slab whose DOS was distributed over a wide energy range. Furthermore, the change in the integrated LDOS correlated well with the O2 adsorption energy on the Pt13 sub-nanocluster.

First-principles study on unidirectional proton transfer on anatase TiO2 (101) surface induced by external electric fields.

The electric field (EF) effect on hydrogen or proton transfer (PT) via hydroxyl groups on an anatase TiO2 (101) surface is examined using first-principles density functional theory and the modern theory of polarization. This study focuses on unidirectional surface PT caused by external EFs at various orientations toward the surface. The preferred PT pathway can change depending on the magnitude and direction of the EF. Detailed analysis reveals that the variation in the energy profile with the EF is significantly different from that determined by the classical electric work of an EF carrying a point charge. The EF effect on the energy profile of the PT is governed by the rearrangement of the chemical bond network at the interface between the water molecules and the surface.

Variations in the Photoexcitation Mechanism of an Adsorbed Molecule on a Gold Nanocluster Governed by Interfacial Contact.

We performed first-principles calculations on the optical response of a Au147-azobenzene complex to elucidate the role of the interfacial contact between Au147 and azobenzene. Our calculations of photoexcited electron dynamics for different configurations of azobenzene adsorbed on the Au147 nanocluster revealed that the optical properties of the azobenzene moiety change markedly by the interfacial contact, even if the electronic structure in the ground state is almost unchanged. The optical absorption measured for isolated azobenzene weakens when the Au147-azobenzene interaction increases, while the absorption measured using the light field along the Au147-azobenzene alignment strengthens. The electronic excitation analysis showed that the mechanism of the charge-transfer excitation between Au147 and azobenzene changes remarkably depending on the strength of the interfacial interaction. We revealed that the optical property can be governed by the atomic-scale difference in the adsorption structure of azobenzene on a Au147 nanocluster. This study affords novel insights that could enable the photoexcitation mechanism to be controlled by designing the interface between a metal nanoparticle and a molecule.

Forms of direction change during walking and effect on movement and reaction time.

[Purpose] To elucidate factors that affect walking before and after direction changes and their effects on reaction time by investigating different angles of direction changes. [Participants and Methods] A total of 29 healthy young males and females participated in this study. The task was to walk along a 20-m path and perform three direction changes while walking: straight walking, 45° direction change, and 90° direction change. Step length and probe reaction time (P-RT) were measured before and after the point of direction change. A two-factor repeated measures analysis of variance was applied to measure P-RT and step length before and after direction changes. [Results] A significant effect was observed for step length and P-RT immediately before and after direction changes. An interaction was also observed between the angle of direction change and the step length before and after the direction change. When compared with the straight walk, a significant effect was observed at 45° and 90° direction changes. [Conclusion] While walking, 90° direction changes are suggested to be more difficult than 45° direction changes, and 45° direction changes are more difficult than walking in a straight line.

Realization of red shift of absorption spectra using optical near-field effect.

In many applications such as CO2 reduction and water splitting, high-energy photons in the ultraviolet region are required to complete the chemical reactions. However, to realize sustainable development, the photon energies utilized must be lower than the absorption edge of the materials including the metal complex for CO2 reduction, the electrodes for water splitting, because of the huge amount of lower energy than the visible region received from the sun. In the previous works, we had demonstrated that optical near-fields (ONFs) could realize chemical reactions, by utilizing photon energies much lower than the absorption edge because of the spatial non-uniformity of the electric field. In this paper, we demonstrate that an ONF can realize the red shift of the absorption spectra of the metal-complex material for photocatalytic reduction. By attaching the metal complex to ZnO nano-crystalline aggregates with nano-scale protrusions, the absorption spectra by using diffuse reflection of the metal complex can be shifted to a longer wavelength by 10.6 nm. The results of computational studies based on a first-principles computational program including the ONF effect provide proof of the increase in the absorption of the metal complex at lower photon energies. Since the near-field assisted field increase improves the carrier excitation in the metal-complex materials, this effect may be universal and it could applicable to CO2 reduction using the other metal-complex materials, as well as to the other photo excitation process including water splitting.

Development of theoretical approach for describing electronic properties of hetero-interface systems under applied bias voltage.

We have developed a theoretical approach for describing the electronic properties of hetero-interface systems under an applied electrode bias. The finite-temperature density functional theory is employed for controlling the chemical potential in their interfacial region, and thereby the electronic charge of the system is obtained. The electric field generated by the electronic charging is described as a saw-tooth-like electrostatic potential. Because of the continuum approximation of dielectrics sandwiched between electrodes, we treat dielectrics with thicknesses in a wide range from a few nanometers to more than several meters. Furthermore, the approach is implemented in our original computational program named grid-based coupled electron and electromagnetic field dynamics (GCEED), facilitating its application to nanostructures. Thus, the approach is capable of comprehensively revealing electronic structure changes in hetero-interface systems with an applied bias that are practically useful for experimental studies. We calculate the electronic structure of a SiO2-graphene-boron nitride (BN) system in which an electrode bias is applied between the graphene layer and an electrode attached on the SiO2 film. The electronic energy barrier between graphene and BN is varied with an applied bias, and the energy variation depends on the thickness of the BN film. This is because the density of states of graphene is so low that the graphene layer cannot fully screen the electric field generated by the electrodes. We have demonstrated that the electronic properties of hetero-interface systems are well controlled by the combination of the electronic charging and the generated electric field.

Gold Quantum Boxes: On the Periodicities and the Quantum Confinement in the Au28, Au36, Au44 , and Au52 Magic Series.

Revealing the size-dependent periodicities (including formula, growth pattern, and property evolution) is an important task in metal nanocluster research. However, investigation on this major issue has been complicated, as the size change is often accompanied by a structural change. Herein, with the successful determination of the Au44(TBBT)28 structure, where TBBT = 4-tert-butylbenzenethiolate, the missing size in the family of Au28(TBBT)20, Au36(TBBT)24, and Au52(TBBT)32 nanoclusters is filled, and a neat "magic series" with a unified formula of Au8n+4(TBBT)4n+8 (n = 3-6) is identified. Such a periodicity in magic numbers is a reflection of the uniform anisotropic growth patterns in this magic series, and the n value is correlated with the number of (001) layers in the face-centered cubic lattice. The size-dependent quantum confinement nature of this magic series is further understood by empirical scaling law, classical "particle in a box" model, and the density functional theory calculations.

Electric field effects on the electronic properties of the silicene-amine interface.

We performed first-principles studies of electric field (EF) effects on the electronic properties of silicene-amine (NH3 and NH2CH3) hetero-interface systems focusing on the electronic interactions at the interface. The band gaps of the systems increase with a positive applied EF but decrease with a negative EF; that is, the band gaps monotonically vary on changing the applied EF from negative to positive. The phenomenon of band gap variation with the sign of the applied EF is a characteristic feature of hetero-interface systems. We revealed the mechanism of the electronic structure change in silicene-amine due to an applied EF by visualizing the electron density change. It is shown that the electronic polarizations in both the Si-N chemical bond region and the silicene-layer region determine the characteristic band gap variation. Furthermore, the tunable energy range of the band gap of the silicene-amine is considerably higher than the range of a silicene monolayer; thus, the idea of controlling the band gaps of hetero-interface systems in combination with application of an EF bias is suitable for designing various devices that are difficult to fabricate with homogeneous two-dimensional materials such as silicene and graphene.

Control of optical response of a supported cluster on different dielectric substrates.

We develop a computational method for optical response of a supported cluster on a dielectric substrate. The substrate is approximated by a dielectric continuum with a frequency-dependent dielectric function. The computational approach is based on our recently developed first-principles simulation method for photoinduced electron dynamics in real-time and real-space. The approach allows us to treat optical response of an adsorbate explicitly taking account of interactions at an interface between an adsorbate and a substrate. We calculate optical absorption spectra of supported Agn (n = 2, 54) clusters, changing the dielectric function of a substrate. By analyzing electron dynamics in real-time and real-space, we clarify the mechanisms for variations in absorption spectra, such as peak shifts and intensity changes, relating to various experimental results for optical absorption of supported clusters. Attractive and repulsive interactions between an adsorbate and a substrate result in red and blue shifts, respectively, and the intensity decreases by energy dissipation into a substrate. We demonstrate that optical properties can be controlled by varying the dielectric function of a substrate.

First-principles computational visualization of localized surface plasmon resonance in gold nanoclusters.

Cluster-size dependence of localized surface plasmon resonance (LSPR) for Aun nanoclusters (n = 54, 146, 308, 560, 922, 1414) is investigated by using our recently developed computational program of first-principles calculations for photoinduced electron dynamics in nanostructures. The size of Au1414 (3.9 nm in diameter) is unprecedentedly large in comparison with those addressed in previous first-principles calculations of optical response in nanoclusters. These computations enable us to clearly see that LSPR gradually grows and the LSPR peaks red shift with increasing cluster size. The growth of LSPR is visualized in real space, demonstrating that electron charge distributions oscillate in a collective manner around the outermost surface region of the clusters. We further illustrate that the core d electrons screen the collective oscillation of the conduction-like s electrons.

Theoretical approach for optical response in electrochemical systems: application to electrode potential dependence of surface-enhanced Raman scattering.

We propose a theoretical approach for optical response in electrochemical systems. The fundamental equation to be solved is based on a time-dependent density functional theory in real-time and real-space in combination with its finite temperature formula treating an electrode potential. Solvation effects are evaluated by a dielectric continuum theory. The approach allows us to treat optical response in electrochemical systems at the atomistic level of theory. We have applied the method to surface-enhanced Raman scattering (SERS) of 4-mercaptopyridine on an Ag electrode surface. It is shown that the SERS intensity has a peak as a function of the electrode potential. Furthermore, the real-space computational approach facilitates visualization of variation of the SERS intensity depending on an electrode potential.

The relationship between flow experience and sense of coherence: a 1-year follow-up study.

This study examined the relationship between flow experience and sense of coherence in 279 tai chi practitioners aged 67.9 ± 7.9 years, with a 1-year follow-up questionnaire. Our results suggest that tai chi improves sense of coherence in older adults, beginners, and long-term practitioners.

Intrinsic Visible Plasmonic Properties of Colloidal PtIn2 Intermetallic Nanoparticles.

Materials that intrinsically exhibit localized surface plasmon resonance (LSPR) in the visible region have been predominantly researched on nanoparticles (NPs) composed of coinage metals, namely Au, Ag, and Cu. Here, as a coinage metal-free intermetallic NPs, colloidal PtIn2 NPs with a C1 (CaF2 -type) crystal structure are synthesized by the liquid phase method, which evidently exhibit LSPR at wavelengths similar to face-centered cubic (fcc)-Au NPs. Computational simulations pointed out differences in the electronic structure and photo-excited electron dynamics between C1-PtIn2 and fcc-Au NPs; reduces interband transition and stronger screening with smaller number of bound d-electrons compare with fcc-Au are unique origins of the visible plasmonic nature of C1-PtIn2 NPs. These results strongly indicate that the intermetallic NPs are expected to address the development of alternative plasmonic materials by tuning their crystal structure and composition.

Development of open-boundary cluster model approach for electrochemical systems and its application to Ag+ adsorption on Au(111) and Ag(111) electrodes.

We present a theoretical method to investigate electrochemical processes on the basis of a finite-temperature density functional theory (FT-DFT) approach combined with our recently developed open-boundary cluster model (OCM). A semi-infinite electrode is well mimicked by a finite-sized simple cluster with an open quantum boundary condition rationalized by OCM. An equilibrium state between adsorbates and an electrode is described by the grand canonical formulation of FT-DFT. These implements allow us to calculate electronic properties of an adsorbate and electrode system at a constant chemical potential µ, i.e., electrode potential. A solvation effect is approximated by a conductor-like polarized continuum model. The method is applied to the electrochemical processes of Ag(+) adsorption on Au(111) and Ag(111). The present constant µ approach has proved essential to electrochemical systems, demonstrating that the method qualitatively reproduces the experimental evidence that Ag(+) adsorbs more on the Au electrode than the Ag one, while the conventional quantum chemistry approach with a constant number of electrons incorrectly gives exactly the opposite result.

Relationships between flow experience, IKIGAI, and sense of coherence in Tai chi practitioners.

The purpose of this study was to examine the mental health effects of Tai chi on regular practitioners by investigating the relationships between flow experience, IKIGAI (Japanese: "Life worth living"), and sense of coherence. The results indicated that flow experience may influence IKIGAI and IKIGAI may influence sense of coherence; this suggests that IKIGAI may act as an intermediary between flow experience and sense of coherence. The results also indicated that the longer the Tai chi experience, the higher was the flow experience.

Pt17 nanocluster electrocatalysts: preparation and origin of high oxygen reduction reaction activity.

We recently found that [Pt17(CO)12(PPh3)8]z (Pt = platinum; CO = carbon monoxide; PPh3 = triphenylphosphine; z = 1+ or 2+) is a Pt nanocluster (Pt NC) that can be synthesized with atomic precision in air. The present study demonstrates that it is possible to prepare a Pt17-supported carbon black (CB) catalyst (Pt17/CB) with 2.1 times higher oxygen reduction reaction (ORR) activity than commercial Pt nanoparticles/CB by the adsorption of [Pt17(CO)12(PPh3)8]z onto CB and subsequent calcination of the catalyst. Density functional theory calculation strongly suggests that the high ORR activity of Pt17/CB originates from the surface Pt atoms that have an electronic structure appropriate for the progress of ORR. These results are expected to provide design guidelines for the fabrication of highly active ORR catalysts using Pt NCs with a diameter of about 1 nm and thereby enabling the use of reduced amounts of Pt in polymer electrolyte fuel cells.

Theoretical study on ionization process in aqueous solution.

Ionization potential (ionization energy) is a fundamental quantity characterizing electronic structure of a molecule. It is known that the energy in solution phase is significantly different from that in the gas phase. In this report, vertical and adiabatic ionization processes in aqueous solution are studied based on a hybrid method of quantum chemistry and statistical mechanics called reference interaction site model-SCF-spacial electron density distribution method. A role of solvation effect is elucidated through molecular level information, i.e., solvent distribution function around solute molecule. By utilizing the linear response regime, a simple expression to evaluate the spectral width from the distribution function is proposed and compared with experimental data.

An extended formula of site-site Smoluchowski-Vlasov equation for electrolyte solution and infinitely dilute solution.

Solvation dynamics is one of the central subjects in solution chemistry. Site-site Smoluchowski-Vlasov (SSSV) equation is a diffusion equation for molecular liquid to analytically calculate the van Hove time correlation function. However, the application has been limited to simple solvent system such as liquid water because of the difficulty in solving the equation. In this study, an extended treatment of SSSV equation is proposed, which is applicable to a wide range of solution systems including mixed solution, electrolyte solution, and infinitely dilute solution. The present treatment realizes computation of the dynamics in LiCl aqueous solution, NaCl aqueous solution, and infinitely dilute aqueous solution of Li(+) and Cs(+) at the molecular level.

A theory for time-dependent solvation structure near solid-liquid interface.

We propose a theory to describe time-dependent solvation structure near solid-liquid interface. Recently, we have developed two-dimensional-reference interaction site model to describe solvation structure near solid-liquid interface at the equilibrium state. In the present study, the theory is extended to treat dynamical aspect of the solvation; site-site Smoluchowski-Vlasov equation and surrogate Hamiltonian description are utilized to deal with the time-dependency. This combination enables us to access a long-time behavior of solvation dynamics. We apply the theory to a model system consisting of an atomistic wall and water solvent, and discuss the hydration structure dynamics near the interface at the molecular-level.

A two-dimensional-reference interaction site model theory for solvation structure near solid-liquid interface.

We develop a new equation to describe solvation structure near solid-liquid interface at the atomic-level. The developed equation focuses on anisotropy of solvation structure near the interface by using two-dimensional density distribution of solvent along two directions, one of which is perpendicular to the interface and the other is parallel to the interface. As a first application of the equation, we treat a system where a solid modeled by an atomistic wall is immersed in solvent water. The preferential adsorption position of water molecules and the change of water orientation by charging the wall are discussed.