Abstract
An expression for the square of the spin operator expectation value, \(\langle{S^{2}}\rangle\), is obtained for a general complex Hartree–Fock wave function and decomposed into four contributions: the main one whose expression is formally identical to the restricted (open-shell) Hartree–Fock expression. A spin contamination one formally analogous to that found for spin unrestricted Hartree–Fock wave functions. A noncollinearity contribution related to the fact that the wave function is not an eigenfunction of the spin-S z operator. A perpendicularity contribution related to the fact that the spin density is not constrained to be zero in the xy - plane. All these contributions are evaluated and compared for the H2O+ system. The optimization of the collinearity axis is also considered.
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Published as part of the special collection of articles “Festschrift in honour of P. R. Surjan.”
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© 2016 Springer-Verlag Berlin Heidelberg
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Cassam-Chenaï, P. (2016). Spin contamination and noncollinearity in general complex Hartree–Fock wave functions. In: Szabados, Á., Kállay, M., Szalay, P. (eds) Péter R. Surján. Highlights in Theoretical Chemistry, vol 12. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-49825-5_21
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DOI: https://doi.org/10.1007/978-3-662-49825-5_21
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Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-662-49824-8
Online ISBN: 978-3-662-49825-5
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