Quantum hydrogen vibrational dynamics in LiH: new neutron measurements and variational Monte Carlo simulations

TL;DR

This study combines neutron scattering experiments and quantum Monte Carlo simulations to analyze hydrogen vibrational dynamics in LiH, providing insights into phonon states, kinetic energy, and anharmonic effects at low temperature.

Contribution

It presents the first combined experimental and variational Monte Carlo analysis of hydrogen vibrational dynamics in LiH, highlighting the accuracy of quantum simulations in this context.

Findings

Good agreement between neutron data and Monte Carlo simulations.

Anharmonic effects are not significant in H dynamics at 20 K.

Semi-empirical potentials have limitations discussed.

Abstract

Hydrogen single-particle dynamics in solid LiH at T=20 K has been studied through the incoherent inelastic neutron scattering technique. A careful analysis of the scattering data has allowed for the determination of a reliable hydrogen-projected density of phonon states and, from this, of three relevant physical quantities: mean squared displacement, mean kinetic energy, and Einstein frequency. In order to interpret these experimental findings, a fully-quantum microscopic calculation has been carried out using the variational Monte Carlo method. The agreement achieved between neutron scattering data and Monte Carlo estimates is good. In addition, a purely harmonic calculation has been also performed via the same Monte Carlo code, but anharmonic effects in H dynamics were not found relevant. The possible limitations of the present semi-empirical potentials are finally discussed.