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Phys Rev E Stat Nonlin Soft Matter Phys. 2007 Sep;76(3 Pt 2):036707. Epub 2007 Sep 18.

Accurate forces in quantum Monte Carlo calculations with nonlocal pseudopotentials.

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  • 1Theory of Condensed Matter Group, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.

Abstract

Calculating accurate forces within variational and diffusion Monte Carlo (VMC and DMC) methods is a very challenging problem. We derive expressions for the contribution to the Hellmann-Feynman force from nonlocal pseudopotentials for use within the VMC and DMC methods. Equilibrium bond lengths and harmonic vibrational frequencies are calculated from the Hellmann-Feynman forces and compared with those obtained from the energies at the Hartree-Fock, VMC, and pure DMC levels. Results for five small molecules show that the equilibrium bond lengths obtained from the force and energy calculations differ by less than 0.007 A at the DMC level.

PMID:
17930361
[PubMed]
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