Hydrogen dissociation on the Mg(0001) surface from quantum Monte Carlo calculations

TL;DR

This study employs diffusion Monte Carlo simulations to accurately determine the hydrogen dissociation energy barrier on Mg(0001), providing a benchmark for computational methods and insights into surface reactions.

Contribution

The paper introduces a systematic DMC approach with error control for calculating surface reaction barriers, offering more precise results than standard DFT methods.

Findings

DMC calculates the H2 dissociation barrier as 1.18 ± 0.03 eV.

DFT exchange-correlation functionals vary widely in predicted barriers (0.44 to 1.07 eV).

Errors from system size and other factors can be reduced to ~0.03 eV.

Abstract

We have used diffusion Monte Carlo (DMC) simulations to calculate the energy barrier for H$_2$ dissociation on the Mg(0001) surface. The calculations employ pseudopotentials and systematically improvable B-spline basis sets to expand the single particle orbitals used to construct the trial wavefunctions. Extensive tests on system size, time step, and other sources of errors, performed on periodically repeated systems of up to 550 atoms, show that all these errors together can be reduced to $\sim 0.03$ eV. The DMC dissociation barrier is calculated to be $1.18 \pm 0.03$ eV, and is compared to those obtained with density functional theory using various exchange-correlation functionals, with values ranging between 0.44 and 1.07 eV.