Fast simulation for multi-photon, atomic-ensemble quantum model of linear optical systems addressing the curse of dimensionality.

Photons are elementary particles of light in quantum mechanics, whose dynamics can be difficult to gain detailed insights, especially in complex systems. Simulation is a promising tool to resolve this issue, but it must address the curse of dimensionality, namely, that the number of bases increases exponentially in the number of photons. Here we mitigate this dimensionality scaling by focusing on optical systems composed of linear optical objects, modeled as an ensemble of two-level atoms.

Accurate Multiscale Simulation of Frictional Interfaces by Quantum Mechanics/Green's Function Molecular Dynamics.

Understanding frictional phenomena is a fascinating fundamental problem with huge potential impact on energy saving. Such an understanding requires monitoring what happens at the sliding buried interface, which is almost inaccessible by experiments. Simulations represent powerful tools in this context, yet a methodological step forward is needed to fully capture the multiscale nature of the frictional phenomena.

Fast evaluation technique for the shear viscosity and ionic conductivity of electrolyte solutions.

With the growing need to obtain ideal materials for various applications, there is an increasing interest in computational methods to rapidly and accurately search for materials. Molecular dynamics simulation is one of the successful methods used to investigate liquid electrolytes with high transport properties applied in lithium-ion batteries. However, further reduction in computational cost is required to find a novel material with the desired properties from a large number of combinations.

Synthesis and Ion-Transport Properties of EuKGeO-, CaFeGeO-, and BaCuGeO-Type Oxide-Ion Conductors.

EuKGeO-, CaFeGeO-, and BaCuGeO-type germanates are synthesized by a conventional solid-state method and characterized to reveal their oxide-ion-conducting properties. Materials of the EuKGeO group exhibit oxide-ion conductivity (e.g.

Self-Learning Molecular Design for High Lithium-Ion Conductive Ionic Liquids using Maze Game.

A self-learning artificial intelligence system for an autonomous molecular search was recently utilized in place of laborious material development processes by humans. In this approach, because the evaluation of unsuitable or unrealistic candidates considerably decreases the search efficiency, prior knowledge of the chemistry and engineering requirements should be embedded into the molecular-generative algorithm. However, when using naive rule-based restrictions, one must implement the complex rule logic into the code each time, depending on the materials and potential applications.

Search for high-capacity oxygen storage materials by materials informatics.

Oxygen storage materials (OSMs), such as pyrochlore type CeO-ZrO (p-CZ), are used as a catalyst support for three-way catalysts in automotive emission control systems. They have oxygen storage capacity (OSC), which is the ability to release and store oxygen reversibly by the fluctuation of cation oxidation states depending on the reducing or oxidizing atmosphere. In this study, we explore high-capacity OSMs by using materials informatics (MI) combining experiments, first-principles calculations, and machine learning (ML).

A Universal 3D Voxel Descriptor for Solid-State Material Informatics with Deep Convolutional Neural Networks.

Material informatics (MI) is a promising approach to liberate us from the time-consuming Edisonian (trial and error) process for material discoveries, driven by machine-learning algorithms. Several descriptors, which are encoded material features to feed computers, were proposed in the last few decades. Especially to solid systems, however, their insufficient representations of three dimensionality of field quantities such as electron distributions and local potentials have critically hindered broad and practical successes of the solid-state MI.

Nanotribological Characterization of Lubricants between Smooth Iron Surfaces.

We performed the resonance shear measurement (RSM) for evaluating the nanorheological and tribological properties of model lubricants, hexadecane and poly(α-olefin) (PAO), confined between iron surfaces. The twin-path surface forces apparatus (SFA) was used for determining the distance between the surfaces. The obtained resonance curves for the confined lubricants showed that the viscosity of the confined hexadecane and PAO increased due to liquid structuring when the surface separation (D) decreased to a value less than 24 and 20 nm, respectively.

Green's function nonequilibrium molecular dynamics method for solid surfaces and interfaces.

This study presents a comprehensive procedure to calculate the exact dynamic Green's function of a harmonic semi-infinite solid and the time trajectories of the atoms, in the framework of the Green's function molecular dynamics. This Green's function properly describes the energy dissipation caused by excitations of the surface phonons, and the simulated atoms serve as well-defined thermo- and barostats for the nonequilibrium surface and interface systems. Moreover, the use of the exact dynamic Green's function coupled with a fast convolution algorithm significantly improves both the accuracy and the computing speed.

Tunneling Desorption of Single Hydrogen on the Surface of Titanium Dioxide.

We investigated the reaction mechanism of the desorption of single hydrogen from a titanium dioxide surface excited by the tip of a scanning tunneling microscope (STM). Analysis of the desorption yield, in combination with theoretical calculations, indicates the crucial role played by the applied electric field. Instead of facilitating desorption by reducing the barrier height, the applied electric field causes a reduction in the barrier width, which, when coupled with the electron excitation induced by the STM tip, leads to the tunneling desorption of the hydrogen.

Mechanism of ultra low friction of multilayer graphene studied by coarse-grained molecular simulation.

Coarse-grained Metropolis Monte Carlo Brownian Dynamics simulations are used to clarify the ultralow friction mechanism of a transfer film of multilayered graphene sheets. Each circular graphene sheet consists of 400 to 1,000,000 atoms confined between the upper and lower sliders and are allowed to move in 3 translational and 1 rotational directions due to thermal motion at 300 K. The sheet-sheet interaction energy is calculated by the sum of the pair potential of the sp2 carbons.

First-principles calculations of hydrogen diffusion on rutile TiO2(110) surfaces.

Density functional calculations are performed to study the H-atom diffusion on titanium dioxide (110) surface in the cases of water-molecule dissociation and splitting of the adjacent hydroxyl OH pair. It is shown that, when a water molecule is adsorbed at a surface oxygen-vacancy site, a fragment H atom of the water molecule tends to diffuse toward the nearest-neighboring bridging-oxygen sites by using a straight-line or relay-point path. As the result, a pair of surface hydroxyl OH is formed on the same oxygen row.