Ab initio free energy calculation of superionic ice

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K04043
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Ehime University
• Principal Investigator: Tsuchiya Jun 愛媛大学, 地球深部ダイナミクス研究センター, 准教授 (00527608)
• Co-Investigator(Kenkyū-buntansha): 土屋 卓久 愛媛大学, 地球深部ダイナミクス研究センター, 教授 (70403863)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 氷超イオン相 / 氷惑星 / 第一原理 / 自由エネルギー

Outline of Final Research Achievements

Determining the structure and physical properties of ice is an important, ongoing issue in physics, chemistry, geophysics, and planetary science. At extreme high pressure and temperature conditions above 100 GPa and ~2000 K, the existence of the superionic ice has been suggested. However, the structure and physical properties of superionic ice phase are still unknown. Here we conducted the ab initio molecular dynamics calculation and found that BCC sublattice of oxygen rotate anomalously above 2500 K at 100-500 GPa. We also developed a program to apply first-principles thermodynamic integration method to the superionic phase and calculated the free energy. In addition, first-principles path integral molecular dynamics calculations were performed taking into account the quantum effects of hydrogen nuclei, and it was found that the quantum effects of nuclei have a non-negligible influence on the elasticity of high pressure ice phases.

Free Research Field

鉱物物理学

Academic Significance and Societal Importance of the Research Achievements

本研究は、液体と固体の両方の性質をもつ氷超イオン相の自由エネルギー計算を参照系から第一原理系（現実系）への直接の熱力学積分により効率的かつ精度よく行う(第一原理熱力学積分法)計算手法開発を行う。この手法は、氷の超イオン相が主要な構成物質の可能性がある氷惑星内部構造を調べる上で重要であるため、惑星科学分野において学術的創造性、重要性を持っている。このような自由エネルギー計算法の開発およびそれによる物性の決定は計算科学・物質科学としても非常に重要かつ挑戦的な課題である。