Journal of Physics: Condensed Matter 22, 074202 (2010)

Methods for calculating forces within quantum Monte Carlo

A. Badinski1,2, P. D. Haynes1,3, J. R. Trail1,4 and R. J. Needs1

1Theory of Condensed Matter Group, Cavendish Laboratory, Cambridge CB3 0HE, UK
2Scientific Computing Group, BASF SE, 67056 Ludwigshafen, Germany
3Department of Physics, Imperial College London, Exhibition Road, London SW7 2AZ, UK
4Japan Advanced Institute of Science and Technology, School of Information Science, Asahidai 1-1, Nomi, Ishikawa 923-1292, Japan

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.

Last updated: 5 August 2010