Quasidegenerate perturbation theory with multiconfigurational self-consistent-field reference functions

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A quasidegenerate perturbation theory based on multiconfigurational self-consistent-field (MCSCF) reference functions is derived. The perturbation theory derived here is for multistate, where several MGSCF functions obtained by the state-averaged MCSCF method are used as the reference and an effective Hamiltonian is constructed by perturbation calculation. The energies of states interested in are obtained simultaneously by diagonalization of the effective Hamiltonian. An explicit formula of the effective Hamiltonian through second order is derived as well as general formalism, and is applied to calculate potential curves of the system H2, Be-H2, CO, NO, BN, and LiF. The results agree well with those of full configuration interaction or multireference single and double excitation configuration interaction methods for both the ground and the excited states.

Original languageEnglish
Pages (from-to)7983-7992
Number of pages10
JournalThe Journal of Chemical Physics
Issue number10
Publication statusPublished - 1993
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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