Quantum Monte Carlo study of the Ne atom and the Ne+ ion

TL;DR

This study uses quantum Monte Carlo methods to accurately calculate the ground-state energies and ionization potential of neon and its ion, exploring different wave function approximations and error cancellations.

Contribution

It demonstrates the effectiveness of various trial wave functions, including backflow correlations, in improving energy estimates and ionization potential calculations.

Findings

Backflow correlations significantly reduce energy errors.

Errors tend to cancel when calculating ionization potential.

DMC provides highly accurate ionization potentials for Ne.

Abstract

We report all-electron and pseudopotential calculations of the ground-stateenergies of the neutral Ne atom and the Ne+ ion using the variational and diffusion quantum Monte Carlo (DMC) methods. We investigate different levels of Slater-Jastrow trial wave function: (i) using Hartree-Fock orbitals, (ii) using orbitals optimized within a Monte Carlo procedure in the presence of a Jastrow factor, and (iii) including backflow correlations in the wave function. Small reductions in the total energy are obtained by optimizing the orbitals, while more significant reductions are obtained by incorporating backflow correlations. We study the finite-time-step and fixed-node biases in the DMC energy and show that there is a strong tendency for these errors to cancel when the first ionization potential (IP) is calculated. DMC gives highly accurate values for the IP of Ne at all the levels of trial wave function that we have considered.