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Examination of the limits of accuracy of the extended Koopmans' theorem ionization potentials into excited states of ions of liH, He 2 , and Li 2
Author(s) -
Morrison Robert C.,
Dixon Christopher M.,
Mizell Jerry R.
Publication year - 1994
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560520832
Subject(s) - atomic physics , excited state , ionization , ion , ionization energy , chemistry , physics , molecular orbital , molecule , quantum mechanics
A comparison is made between the ionization potentials ( IPS ) calculated by the extended Koopmans' theorem ( EKT ) and by taking energy differences (Δ CI ) from configuration interaction calculations in the same basis. Several ionization potentials were calculated for LiH, He 2 , and Li 2 . The best Δ IP , the difference between the EKT IP and the corresponding Δ CI value, was 0.05 meV for the 2σ orbital for LiH and 83.5 meV for the 3σ orbital. The Δ IPS for He 2 were 0.7 meV for the 1σ u orbital, 6 eV for the 2σ u orbital, 5 meV for the 2σ g orbital, and 3 eV for the 3σ g orbital. The Δ IPS for Li 2 are 0.1 meV for 2σ g , 53 meV for 3σ g , 0.6 meV for 2σ u , and 1.73 eV for 3σ u . © 1994 John Wiley & Sons, Inc.