Quantum and temperature effects on crystal structure of superhydride: A path integral molecular dynamics study

TL;DR

This study uses molecular dynamics simulations to explore how quantum and thermal effects influence the crystal structure of LaH$_{10}$ under various pressures and temperatures, revealing conditions that stabilize superconducting phases.

Contribution

It provides new insights into the combined impact of temperature and quantum effects on the crystal structure and phase stability of superhydrides, especially LaH$_{10}$, using path-integral molecular dynamics.

Findings

Temperature stabilizes the high-symmetry $Fm\bar{3}m$ structure at certain pressures.

Quantum effects are crucial at lower temperatures for structure stabilization.

The system approaches a phase transition near 100 GPa and 300 K.

Abstract

By classical and path-integral molecular dynamics simulations, we study the pressure-temperature ($P$-$T$) phase diagram of LaH$_{10}$ to clarify the impact of temperature and atomic zero-point motions. We calculate the XRD pattern and analyze the space group of the crystal structures. For 125 GPa $\leq P\leq$ 150 GPa and $T=300$ K, we show that a highly symmetric $Fm\bar{3}m$ structure, for which superconductivity is particularly favored, is stabilized only by the temperature effect. On the other hand, for $T=200$ K, the interplay between the temperature and quantum effects is crucial to realize the $Fm\bar{3}m$ structure. For $P=$100 GPa and $T=$300 K, we find that the system is close to the critical point of the structural phase transition between the $Fm\bar{3}m$ structure and those with lower symmetries.