Spin-Unrestricted Calculations in Quantum Chemistry

P. Cassam-Chenai, Graham Chandler

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23 Citations (Web of Science)


The unrestricted complete active space self-consistent field (UCASSCF) function is defined, and a proof that a UCASSCF eigenfunction of the spin operator S2 is a CASSCF function is given. The spin-contamination for an unrestricted Hartree-Fock (UHF) function is evaluated by using Araki angle operators, and the UHF function is then projected on the restricted open-shell Hartree-Fock (ROHF) space. The present analysis has deep consequences since it implies that the only non-spin-contaminated UHF functions are the ROHF functions. This is illustrated in a calculation of the spin density of He2+.
Original languageEnglish
Pages (from-to)593-607
JournalInternational Journal of Quantum Chemistry
Publication statusPublished - 1993


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