Wave functions for quantum Monte Carlo calculations in solids: Orbitals from density functional theory with hybrid exchange-correlation functionals

TL;DR

This paper explores how the choice of single-particle orbitals from density functional theory affects the accuracy of fixed-node diffusion Monte Carlo calculations in solids, especially for transition-metal compounds, and suggests ways to optimize these orbitals to reduce errors.

Contribution

It demonstrates the significant impact of orbital choice on Monte Carlo energies and introduces a method to optimize orbitals using exchange-correlation functionals with variable exact exchange.

Findings

Dependence of fixed-node DMC energy on orbitals is significant in 3d transition-metal compounds.

Adjusting the exchange component in functionals can reduce fixed-node errors.

Fixed-node QMC can be used to optimize effective Hamiltonian parameters.

Abstract

We investigate how the fixed-node diffusion Monte Carlo energy of solids depends on single-particle orbitals used in Slater--Jastrow wave functions. We demonstrate that the dependence can be significant, in particular in the case of 3d transition-metal compounds, which we adopt as examples. We illustrate how exchange-correlation functionals with variable exact-exchange component can be exploited to reduce the fixed-node errors. On the basis of these results we argue that the fixed-node quantum Monte Carlo provides a variational approach for optimization of effective hamiltonians with parameters.