[S-CG49] Innovation through the Integration of Solid Earth Science and Materials Science

[SCG49-P04] First-principles path integral molecular dynamics calculations of the equation of state and elastic properties of NaCl-bearing high pressure Ice

*Jun Tsuchiya¹, Haruhiko Dekura¹, Motoyuki Shiga² (1.Geodynamics Research Center, Ehime University, 2.Japan Atomic Energy Agency)

The high pressure phase transition from ice VII to ice X goes from static proton disorder to dynamic disorder to a symmetric hydrogen-bonded state above about 100 GPa. Many high-pressure experiments and theoretical calculations have been performed to investigate the equation of state and physical properties of this system. In particular, an increase in the compressibility (Sugimura et al. 2008) of the equation of state of phase VII at around 40-60 GPa have been observed, which may be due to the dynamic proton disorder state. It has been suggested that quantum effects of hydrogen nuclei have a non-negligible influence on the compressive behavior, vibrational properties, elasticity, etc. On the other hand, high-pressure ice containing a few percent salt (NaCl) has been reported to show no such quantum effects and to increase the phase transition pressure to the ice X phase by about 30 GPa (e.g. Bronstein et al. 2016, Bove et al. 2015). Also, the elastic constants of the NaCl-containing ice phase VII are reported to soften around 40-50 GPa (Shi et al. 2021).
First-principles molecular dynamics calculations are an effective tool to investigate the change of state of protons under high pressure, which is difficult to do experimentally; however, the quantum effects of hydrogen nuclei have not been taken into account. In this study, we performed first-principles molecular dynamics and first-principles path integral molecular dynamics calculations to investigate the proton state change from NaCl bearing high pressure ice VII to X, taking into account the quantum effects of the nucleus. This study compares our previous equation of state and elastic properties of pure high-pressure ice with those of salt-containing high-pressure ice to determine how the equation of state and elastic constants of salt-containing high-pressure ice differ.