Methods for calculating forces within quantum Monte Carlo simulations

TL;DR

This paper discusses methods for calculating atomic forces in quantum Monte Carlo simulations, emphasizing the advantages of using the pure distribution and presenting a practical approach tested on SiH.

Contribution

It introduces a new practical method for calculating forces using the pure distribution in quantum Monte Carlo, with analysis of estimator statistics and limitations.

Findings

Pure distribution force calculations are more accurate.

Violations of the Central Limit Theorem occur in some cases.

Method successfully tested on SiH molecule.

Abstract

Atomic force calculations within the variational and diffusion quantum Monte Carlo (VMC and DMC) methods are described. The advantages of calculating DMC forces with the "pure" rather than the "mixed" probability distribution are discussed. An accurate and practical method for calculating forces using the pure distribution is presented and tested for the SiH molecule. The statistics of force estimators are explored and violations of the Central Limit Theorem are found in some cases.