First Principles Isothermal-Isobaric Centroid Molecular Dynamics Simulation of High Pressure Ices

We performed Born-Oppenheimer (BO) centroid molecular dynamics (CMD) simulations in the NPT ensemble for high pressure ices VIII, VII, and X at 270 K to assess the performance of our implemented first principles isothermal-isobaric CMD. We observed that the crystal system of H2O ice successfully transforms from tetragonal to cubic at ~30 GPa in our isothermal-isobaric BO-CMD simulations by elevating pressure at 270 K, consistent with the transition from proton-ordered ice VIII to proton-disordered ice VII actually observed to occur in our simulations. Moreover, we found that our simulations are able to reproduce well both infrared and Raman spectra for high pressure ices in the frequency range above ~500 cm-1 once the adiabatic separation of the fictitious dynamics of the simulation cell from the intrinsic vibrations of H2O ices is achieved. These results indicate that our implemented BO-CMD in the NPT ensemble is capable of reproducing the characteristics of the pressure induced two transitions of ice VIII to ice VII and ice VII to ice X, which are triggered by quantum tunneling and zero-point fluctuations of the protons, respectively.4th QST International Symposium -Innovation from Quantum Materials Science