Bulk and surface energetics of lithium hydride crystal: benchmarks from quantum Monte Carlo and quantum chemistry

TL;DR

This study uses quantum Monte Carlo and wavefunction-based quantum chemistry to accurately compute the bulk and surface energetics of lithium hydride, providing benchmark values that agree closely with experimental data.

Contribution

It demonstrates high-precision calculations of lithium hydride's bulk and surface energies using advanced quantum methods, establishing benchmarks for future research.

Findings

Lattice parameter matches experimental value within 0.03%.

Cohesive energy agrees within 10 meV per formula unit.

QMC and quantum chemistry results for surface energy agree within 1%.

Abstract

We show how accurate benchmark values of the surface formation energy of crystalline lithium hydride can be computed by the complementary techniques of quantum Monte Carlo (QMC) and wavefunction-based molecular quantum chemistry. To demonstrate the high accuracy of the QMC techniques, we present a detailed study of the energetics of the bulk LiH crystal, using both pseudopotential and all-electron approaches. We show that the equilibrium lattice parameter agrees with experiment to within 0.03 %, which is around the experimental uncertainty, and the cohesive energy agrees to within around 10 meV per formula unit. QMC in periodic slab geometry is used to compute the formation energy of the LiH (001) surface, and we show that the value can be accurately converged with respect to slab thickness and other technical parameters. The quantum chemistry calculations build on the recently developed hierarchical scheme for computing the correlation energy of a crystal to high precision. We show that the hierarchical scheme allows the accurate calculation of the surface formation energy, and we present results that are well converged with respect to basis set and with respect to the level of correlation treatment. The QMC and hierarchical results for the surface formation energy agree to within about 1 %.