High-Pressure Hydrogen Sulfide by Diffusion Quantum Monte Carlo

TL;DR

This study employs diffusion quantum Monte Carlo to refine the phase diagram of high-pressure H$_2$S and related compounds, revealing new stability ranges and phase transitions that differ from previous density functional theory predictions.

Contribution

The paper provides the first diffusion quantum Monte Carlo analysis of H$_2$S phases at high pressure, revising the enthalpy-pressure phase diagram and identifying the most stable structures.

Findings

C2/c HS$_2$ persists up to 440 GPa before transitioning to C2/m.

C2/m phase of HS is more stable than I4$_1$/amd from 150 to 400 GPa.

Im-3m phase is likely for H$_3$S, aligning with recent experiments.

Abstract

We use the diffusion quantum Monte Carlo to revisit the enthalpy-pressure phase diagram of the various products from the different proposed decompositions of H$_2$S at pressures above 150~GPa. Our results entails a revision of the ground-state enthalpy-pressure phase diagram. Specifically, we find that the C2/c HS$_2$ structure is persistent up to 440~GPa before undergoing a phase transition into the C2/m phase. Contrary to density functional theory, our calculations suggest that the C2/m phase of HS is more stable than the I4$_1$/amd HS structure over the whole pressure range from 150 to 400 GPa. Moreover, we predict that the Im-3m phase is the most likely candidate for H$_3$S, which is consistent with recent experimental x-ray diffraction measurements.