Trail-Needs pseudopotentials in quantum Monte Carlo calculations with plane-wave/blip basis sets

TL;DR

This paper systematically evaluates Dirac-Fock pseudopotentials in quantum Monte Carlo calculations across the periodic table, addressing ghost states, trial wave functions, and optimal computational parameters for improved accuracy.

Contribution

It provides a comprehensive analysis of pseudopotential performance in QMC, offering guidelines for basis set choices and computational schemes to enhance accuracy.

Findings

Ghost states can be mitigated by local channel choices in DFT and QMC.

Optimal trial wave functions reduce energy variance.

The 'T-move' scheme is crucial for many elements.

Abstract

We report a systematic analysis of the performance of a widely used set of Dirac-Fock pseudopotentials for quantum Monte Carlo (QMC) calculations. We study each atom in the periodic table from hydrogen (Z=1) to mercury (Z=80), with the exception of the 4f elements (57 <= Z <= 70). We demonstrate that ghost states are a potentially serious problem when plane-wave basis sets are used in density functional theory (DFT) orbital-generation calculations, but that this problem can be almost entirely eliminated by choosing the s channel to be local in the DFT calculation; the d channel can then be chosen to be local in subsequent QMC calculations, which generally leads to more accurate results. We investigate the achievable energy variance per electron with different levels of trial wave function and we determine appropriate plane-wave cutoff energies for DFT calculations for each pseudopotential. We demonstrate that the so-called "T-move" scheme in diffusion Monte Carlo is essential for many elements. We investigate the optimal choice of spherical integration rule for pseudopotential projectors in QMC calculations. The information reported here will prove crucial in the planning and execution of QMC projects involving beyond-first-row elements.