Development of first principles calculation scheme of thermodynamic phase diagram

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K03673
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 13010:Mathematical physics and fundamental theory of condensed matter physics-related
• Research Institution: Kyushu Institute of Technology
• Principal Investigator: Kazuma Nakamura 九州工業大学, 大学院工学研究院, 教授 (60525236)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 第一原理計算 / 熱力学状態図

Outline of Final Research Achievements

A thermodynamic phase diagram of the transition-metal hydride TiH was calculated with first-principles calculations. The Gibbs free energy consists of three terms; the enthalpy, phonon, and solid-solution entropy terms, which were evaluated by ab initio calculations. The enthalpy term was evaluated by generating a large number of atomic configurations in which hydrogen was partially inserted into the void sites of the Ti metal, and performing first-principles calculations for each structure. Cluster-expansion and cluster-variational methods were performed for these structures to obtain a solid-solution entropy term. The contribution of phonons to the free energy was evaluated from ab initio phonon calculations. A regular solution model for the obtained free energy was constructed, and a thermodynamic phase diagram based on this model was calculated. We obtained a good agreement between the theoretical and experimental results.

Free Research Field

計算物質科学

Academic Significance and Societal Importance of the Research Achievements

金属水素化物の熱力学状態図の作成は，水素脆化の原因究明，新規水素吸蔵合金の探索など，工学的実用性において重要である。これまで状態図作成は実験主導であり，経験的アプローチに基づいて研究が進められてきた。本研究では，第一原理計算による物質の熱力学状態図の作成を行った。第一原理計算に基づくと，熱力学的状態の安定性に関わる各項を個別に評価できるため，相の安定性起源に関する微視的理解が得られる。実験状態図を定量的に再現できる第一原理状態図が得られれば，実験結果の解析において威力を発揮するだけでなく，理論手動で物質・材料設計をリードすることも可能となる。