Title
Self-Refinement of Auxiliary-Field Quantum Monte Carlo via Non-Orthogonal Configuration Interaction
Martin Schlipf
VASP Software GmbH
Abstract
For optimal accuracy, auxiliary-field quantum Monte Carlo (AFQMC) requires trial states consisting of multiple Slater determinants. We develop an efficient algorithm to select the determinants from an AFQMC random walk eliminating the need for other methods. When determinants contribute significantly to the nonorthogonal configuration interaction energy, we include them in the trial state. These refined trial wave functions significantly reduce the phaseless bias and sampling variance of the local energy estimator. With 100 to 200 determinants, we lower the error of AFQMC by up to a factor of 10 for second-row elements that are not accurately described with a Hartree–Fock trial wave function. For the HEAT set, we improve the average error to within chemical accuracy. For benzene, the largest studied system, we reduce AFQMC error by 80% with 214 Slater determinants and find a 10-fold increase of the time to solution. We show that phaseless errors prevail in systems with static correlation or strong spin contamination. For such systems, improved trial states enable stable free-projection AFQMC calculations, achieving chemical accuracy even in the strongly correlated regime.
Keywords
Chemical calculationsDeterminantsEnergyMoleculesWave function
Object type
Language
English [eng]
Persistent identifier
Appeared in
Title
Journal of Chemical Theory and Computation
Volume
21
Issue
9
ISSN
1549-9618
Issued
2025
From page
4481
To page
4493
Publication
American Chemical Society (ACS)
Version type
Date issued
2025
Access rights
Rights
Rights statement
© 2025 The Authors
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