TITLE

Auxiliary-field quantum Monte Carlo calculations of molecular systems with a Gaussian basis

AUTHOR(S)
Al-Saidi, W. A.; Shiwei Zhang; Krakauer, Henry
PUB. DATE
June 2006
SOURCE
Journal of Chemical Physics;6/14/2006, Vol. 124 Issue 22, p224101
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
We extend the recently introduced phaseless auxiliary-field quantum Monte Carlo (QMC) approach to any single-particle basis and apply it to molecular systems with Gaussian basis sets. QMC methods in general scale favorably with the system size as a low power. A QMC approach with auxiliary fields, in principle, allows an exact solution of the Schrödinger equation in the chosen basis. However, the well-known sign/phase problem causes the statistical noise to increase exponentially. The phaseless method controls this problem by constraining the paths in the auxiliary-field path integrals with an approximate phase condition that depends on a trial wave function. In the present calculations, the trial wave function is a single Slater determinant from a Hartree-Fock calculation. The calculated all-electron total energies show typical systematic errors of no more than a few millihartrees compared to exact results. At equilibrium geometries in the molecules we studied, this accuracy is roughly comparable to that of coupled cluster with single and double excitations and with noniterative triples [CCSD(T)]. For stretched bonds in H2O, our method exhibits a better overall accuracy and a more uniform behavior than CCSD(T).
ACCESSION #
21299855

 

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