第一原理計算に基づく合金ナノ粒子の安定構造の予測手法の開発

摘要

実験的パラメータを用いなぃ第一原理計算は近年の計算機と計算技術の発展に伴い，絶対零度における系の内部エネルギーのみではなく，比熱や熱膨張率といった有限温度での物性を定量的に求めることが可能になってきている.しかし二元系以上の合金において相安定性を議論するためには，一般に数千〜数万以上の原子数とそれに対応した数百万以上の原子配置を考慮する必要がある.%Based on the first-principles calculation combined with the cluster expansion technique, we developed a formalism enabling energetics for alloy nanoparticles with multiple shapes to be modeled. One of the essential drawbacks in conventional cluster expansion is that the Hamiltonian of cluster expansion depends on the shape of nanoparticles, which leads to difficulties in modeling more general energetics for nanoparticles. In order to overcome this problem, we introduced the concept of "virtual" vacancy into cluster expansion, which successfully makes the cluster expansion Hamiltonian, independent of the shape. We demonstrate that the proposed formalism can accurately describe the relative energies of alloy nanoparticles with possible composition and atomic configuration of a variety of shapes, which leads to comprehensively addressing a stable as well as metastable structure for alloy nanoparticles.