Ab initio Calculations in Atoms, Molecules, and Solids, Treating Spin-Orbit Coupling and Electron Interaction on Equal Footing

TL;DR

This paper develops a non-perturbative ab initio quantum Monte Carlo method that accurately incorporates spin-orbit coupling and electron correlation for molecules and solids, enabling precise predictions across diverse systems.

Contribution

It introduces a generalized AFQMC framework with relativistic effective-core potentials to treat spin-orbit effects and electron interactions simultaneously.

Findings

Accurate electron affinity calculation for Pb

Precise bond dissociation energies for Br₂ and I₂

Reliable modeling of solid Bi with spin-orbit coupling

Abstract

We incorporate explicit, non-perturbative treatment of spin-orbit coupling into ab initio auxiliary-field quantum Monte Carlo (AFQMC) calculations. The approach allows a general computational framework for molecular and bulk systems in which materials specificity, electron correlation, and spin-orbit coupling effects can be captured accurately and on equal footing, with favorable computational scaling versus system size. We adopt relativistic effective-core potentials which have been obtained by fitting to fully relativistic data and which have demonstrated a high degree of reliability and transferability in molecular systems. This results in a 2-component spin-coupled Hamiltonian, which is then treated by generalizing the ab initio AFQMC approach. We demonstrate the method by computing the electron affinity in Pb, the bond dissociation energy in Br$_2$ and I$_2$, and solid Bi.