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UHF natural orbitals for defining and starting MC-SCF calculations

Pulay, Peter, Hamilton, Tracy P.·1988·The Journal of Chemical Physics

Abstract

A simple way of generating starting orbitals for multiconfigurational SCF calculations (particularly of the CAS type) is to use the natural orbitals of the unrestricted Hartree–Fock wave function. Significant fractional occupancy of a UHF natural orbital indicates that the orbital should be included in the active space; this is illustrated for symmetrically stretched water, for NO, N2O4, and for the transition state on the Me3CO→Me2CO+CH3 reaction surface. Average natural orbitals should be used if there are several UHF solutions for the same state; this restores symmetry broken at the the UHF level. Configuration selection based on fractional occupation appears to be the basis for a reliable automated procedure. The UHF natural orbitals provide good starting orbitals for the two-configuration SCF and for the 4×4 CAS wave function in stretched F2, H2O2, and C2H6, methane, water, in twisted ethylene, in ozone, and for various CAS wave functions in the first asynchronous transition state of the HCNO+H2C2 1,3-cycloaddition. Comparison is made with the extended Hartree–Fock method.

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Metadata

Authors
Pulay, P., & Hamilton, T. P.
Venue
The Journal of Chemical Physics
Published
1988-04-15
Volume
88
Issue
8
Pages
4926-4933
ISSN
  • 0021-9606 (ISSN-L)
  • 1089-7690
OpenAlex
W1999857092
Cited by
276
References
16
FWCI
1.57
Type
journal article
Language
en
Open access
closed

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CoChat. (2026). Citation check: UHF natural orbitals for defining and starting MC-SCF calculations. https://app.cochat.ai/papers/10.1063/1.454704
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Pulay, P., & Hamilton, T. P. (1988). UHF natural orbitals for defining and starting MC-SCF calculations. The Journal of Chemical Physics. https://doi.org/10.1063/1.454704

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