Eliminating spin contamination in auxiliary-field quantum Monte Carlo: realistic potential energy curve of F2

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dc.creatorPurwanto, Wirawan
dc.creatorAl-Saidi, W. A.
dc.creatorKrakauer, Henry
dc.creatorZhang, Shiwei
dc.date2007-12-12
dc.date.accessioned2026-07-07T09:27:16Z
dc.date.available2026-07-07T09:27:16Z
dc.descriptionThe use of an approximate reference state wave function |Phi_r> in electronic many-body methods can break the spin symmetry of Born-Oppenheimer spin-independent Hamiltonians. This can result in significant errors, especially when bonds are stretched or broken. A simple spin-projection method is introduced for auxiliary-field quantum Monte Carlo (AFQMC) calculations, which yields spin-contamination-free results, even with a spin-contaminated |Phi_r>. The method is applied to the difficult F2 molecule, which is unbound within unrestricted Hartree-Fock (UHF). With a UHF |Phi_r>, spin contamination causes large systematic errors and long equilibration times in AFQMC in the intermediate, bond-breaking region. The spin-projection method eliminates these problems, and delivers an accurate potential energy curve from equilibrium to the dissociation limit using the UHF |Phi_r>. Realistic potential energy curves are obtained with a cc-pVQZ basis. The calculated spectroscopic constants are in excellent agreement with experiment.
dc.description8 pages, 6 figures, submitted to J. Chem. Phys
dc.identifierhttps://arxiv.org/abs/0712.1935
dc.identifierhttp://arxiv.org/abs/0712.1935
dc.identifierJ. Chem. Phys. 128, 114309 (2008)
dc.identifierdoi:10.1063/1.2838983
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/157036
dc.subjectComputational Physics
dc.subjectChemical Physics
dc.titleEliminating spin contamination in auxiliary-field quantum Monte Carlo: realistic potential energy curve of F2
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