arXiv subjects

Shunya Yamada

Publications and source records attributed to Shunya Yamada.

3 recordsLinked to original sources

arXiv2026

A Metadynamics-Based Framework for Free Energy Surface Mapping of Multiparticle Diffusion in Crystals

We propose two metadynamics (MetaD)-based methodologies for efficiently mapping free energy surfaces (FESs) of multiple interacting carriers diffusing in crystalline solids. Our approaches circumvent the challenges of high-dimensional collective variables (CVs) by employing replica state exchange MetaD and parallel bias MetaD, both of which decompose the high-dimensional CVs into multiple lower-dimensional ones. As a benchmark, we investigate two-dimensional lithium (Li) diffusion in LixTiS2 across a wide range of Li concentrations. The Li jump frequencies estimated from the obtained FESs exhibit concentration- and temperature-dependent trends consistent with previous kinetic Monte Carlo simulations and nuclear magnetic resonance measurements. Our approaches provide a promising framework for capturing the slow dynamics of diffusive carriers that are typically inaccessible to conventional molecular dynamics simulations.

cond-mat.mtrl-sci↗

arXiv2026

Metadynamics for Vacancy Dynamics in Crystals

We propose a metadynamics-based (MetaD-based) approach to construct the free energy surface (FES) for vacancy dynamics in crystals. In this approach, the vacancy FES can be constructed without explicitly defining a unique vacancy coordinate by introducing a set of parameters that strongly govern the FES, which is enabled by parallel bias MetaD with partitioned families (PB-MetaDPF). In addition, the proposed approach is made more efficient and effective by multihill strategy that exploits crystallographic symmetry. We demonstrate the validity and efficacy of the proposed approach by its applications to self-diffusion and impurity diffusion via monovacancies and divacancies in metallic and ionic crystals.

cond-mat.mtrl-sci↗

arXiv2024

Nuclear Quantum Effects on Proton Diffusivity in Perovskite Oxides

In the present study, the nuclear quantum effects (NQEs) on proton diffusivity in oxides were evaluated by molecular dynamics (MD) simulations with the quantum thermal bath (QTB) based on the Langevin dynamics. We employed the proton diffusion in barium zirconate (BaZrO3) with the cubic perovskite structure as the model system, in which protons migrate by rotation around single oxide ions and hopping between adjacent oxide ions. MD simulations with the standard classical thermal bath (CTB) and phonon calculations were also conducted to verify the conventionally used classical harmonic transition state theory (classical h-TST), in which the transition state theory (TST), the harmonic approximation, and the classical approximation are assumed. As a result, the h-TST are reasonable for the proton rotation, while significantly overestimate the activation energy and the pre-exponential factor of the jump frequency for the proton hopping. Furthermore, the classical approximation makes the proton jump frequencies close to linear in the Arrhenius plots, which should actually be nonlinear by the NQEs in the temperature range of 500-2000 K. This suggests the necessity of the treatment beyond the classical h-TST for accurate evaluation of the proton diffusivity in oxides even in the intermediate temperature range (573-873 K).

cond-mat.mtrl-sci↗