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Extended Koopmans' theorem: Approximate ionization energies from MCSCF wave functions
Author(s) -
Morrison Robert C.,
Liu Guanghua
Publication year - 1992
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540130811
Subject(s) - ionization , wave function , excited state , atomic physics , ionization energy , ion , chemistry , molecule , physics , quantum mechanics
The extended Koopmans' theorem has been implemented using multiconfigurational self‐consistent field wave functions calculated with the GAMESS, HONDO, and SIRIUS programs. The results of illustrative calculations are presented for the molecules HF, H 2 O, NH 3 , CH 4 , N 2 , CO, HNC, HCN, C 2 H 2 , H 2 CO, and B 2 H 6 . The lowest extended Koopmans' theorem ionization potentials agree well within the experimental values and the ionization potentials representing excited states of the ions show some improvements over the Koopmans' theorem values in most cases. The extended Koopmans' theorem is easily implemented and the time required to calculate the ionization energies is insignificant compared to the time required to calculate the wave function of the un‐ionized molecule. © 1992 by John Wiley & Sons, Inc.