Capturing nuclear quantum effects in high-pressure superconducting hydrides and ice with nuclear-electronic orbital theory

TL;DR

This paper demonstrates that nuclear-electronic orbital density functional theory (NEO-DFT) effectively captures nuclear quantum effects in high-pressure hydrides and ice, accurately predicting phase transition pressures and structures with improved efficiency.

Contribution

The study introduces NEO-DFT as a computationally efficient method to accurately include nuclear quantum effects in complex hydrogen-rich materials, outperforming traditional approaches.

Findings

NEO-DFT accurately predicts hydrogen-bond symmetrization pressures in H3S and D3S.

NEO-DFT correctly identifies the structure of LaH10 at various pressures.

The method accurately predicts ice phase transition pressures consistent with experiments.

Abstract

Nuclear quantum effects are essential for correctly describing hydrogen-rich materials at high pressures. Superconducting hydrides and ice are prime examples of such systems, requiring the inclusion of lattice anharmonicity and nuclear quantum effects to correctly predict and describe the structures and phase transition pressures observed experimentally. Herein, we show that the nuclear-electronic orbital density functional theory (NEO-DFT) method, which treats specified nuclei quantum mechanically on the same level as the electrons, is capable of accurately describing nuclear quantum effects in superconducting hydrides and ice. NEO-DFT predicts the hydrogen-bond symmetrization pressure in H$_3$S and D$_3$S, benchmarking against the more expensive stochastic self-consistent harmonic approximation (SSCHA) method, and predicts the correct symmetric Fm$\bar{3}$m structure for LaH$_{10}$ at a wide range of pressures. NEO-DFT also predicts the ice VIII to ice X phase transition pressures for H$_2$O and D$_2$O in agreement with experimental measurements. The accuracy, computational efficiency, and broad applicability of the NEO method opens the door for expanded large-scale studies into these types of systems.