Quantum lattice dynamics and their importance in ternary superhydride clathrates

TL;DR

This paper investigates the quantum effects on the lattice dynamics of superconducting hydrides, showing that anharmonic quantum ionic effects significantly influence the stability and synthesis conditions of BaSiH8.

Contribution

It demonstrates that quantum ionic effects alter the dynamical stability and critical pressure estimates for BaSiH8, providing more accurate predictions for material synthesis.

Findings

Quantum ionic effects increase the critical dynamical pressure from 5 GPa to 20 GPa.

Zero-point energy corrections can predict structural changes at the harmonic level.

Kinetic stability pressure (30 GPa) is a stricter bound than dynamical stability for synthesis.

Abstract

The quantum nature of the hydrogen lattice in superconducting hydrides can have crucial effects on the material's properties. Taking a detailed look at the dynamic stability of the recently predicted BaSiH$_8$ phase, we find that the inclusion of anharmonic quantum ionic effects leads to an increase in the critical dynamical pressure to $20\,\text{GPa}$ as compared to $5\,\text{GPa}$ within the harmonic approximation. We identify the change in the crystal structure due to quantum ionic effects to be the main driving force for this increase and demonstrate that this can already be understood at the harmonic level by considering zero-point energy corrections to the total electronic energy. In fact, the previously determined critical pressure of kinetic stability $p_\text{kin} = 30\,\text{GPa}$ still poses a stricter bound for the synthesizability of BaSiH$_8$ and similar hydride materials than the dynamical stability and therefore constitutes a more rigorous and accurate estimate for the experimental realizability of these structures.