Accurate, efficient and simple forces with Quantum Monte Carlo methods

Abstract

Computation of ionic forces using quantum Monte Carlo methods has long been a challenge. We introduce a simple procedure, based on known properties of physical electronic densities, to make the variance of the Hellmann-Feynman estimator finite. We obtain very accurate geometries for the molecules H${}_2$, LiH, CH${}_4$, NH${}_3$, H${}_2$O and HF, with a Slater-Jastrow trial wave function. Harmonic frequencies for diatomics are also in good agreement with experiment. An antithetical sampling method is also discussed for additional reduction of the variance.

4 pages, 4 figures. Minor changes. Accepted for publication on PRL