The diffusion Monte Carlo (DMC), auxiliary field quantum Monte Carlo (AFQMC), and equation-of-motion coupled cluster (EOM-CC) methods are used to calculate the electron binding energy (EBE) of the non-valence anion state of a model (H2O)4 cluster. Two geometries are considered, one at which the anion is unbound and the other at which it is bound in the Hartree–Fock (HF) approximation. It is demonstrated that DMC calculations can recover from the use of a HF trial wave function that has collapsed onto a discretized continuum solution, although larger EBEs are obtained when using a trial wave function for the anion that provides a more realistic description of the charge distribution and, hence, of the nodal surface. For the geometry at which the cluster has a non-valence correlation-bound anion, both the inclusion of triples in the EOM-CC method and the inclusion of supplemental diffuse d functions in the basis set are important. DMC calculations with suitable trial wave functions give EBE values in good agreement with our best estimate EOM-CC result. AFQMC using a trial wave function for the anion with a realistic electron density gives a value of the EBE nearly identical to the EOM-CC result when using the same basis set. For the geometry at which the anion is bound in the HF approximation, the inclusion of triple excitations in the EOM-CC calculations is much less important. The best estimate EOM-CC EBE value is in good agreement with the results of DMC calculations with appropriate trial wave functions.
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14 December 2020
Research Article|
December 14 2020
The role of high-order electron correlation effects in a model system for non-valence correlation-bound anions
Special Collection:
Frontiers of Stochastic Electronic Structure Calculations
Shiv Upadhyay
;
Shiv Upadhyay
1
Department of Chemistry, University of Pittsburgh
, Pittsburgh, Pennsylvania 15260, USA
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Amanda Dumi
;
Amanda Dumi
1
Department of Chemistry, University of Pittsburgh
, Pittsburgh, Pennsylvania 15260, USA
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James Shee
;
James Shee
2
Department of Chemistry, University of California Berkeley
, Berkeley, California 94720, USA
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Kenneth D. Jordan
Kenneth D. Jordan
a)
1
Department of Chemistry, University of Pittsburgh
, Pittsburgh, Pennsylvania 15260, USA
a)Author to whom correspondence should be addressed: [email protected]
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a)Author to whom correspondence should be addressed: [email protected]
Note: This paper is part of the JCP Special Topic on Frontiers of Stochastic Electronic Structure Calculations.
J. Chem. Phys. 153, 224118 (2020)
Article history
Received:
September 25 2020
Accepted:
November 22 2020
Citation
Shiv Upadhyay, Amanda Dumi, James Shee, Kenneth D. Jordan; The role of high-order electron correlation effects in a model system for non-valence correlation-bound anions. J. Chem. Phys. 14 December 2020; 153 (22): 224118. https://doi.org/10.1063/5.0030942
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