Premium
Direct calculation of excitation energies by the coupled‐cluster method: Mg and Ar atoms
Author(s) -
Kaldor Uzi
Publication year - 1986
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.560300739
Subject(s) - excitation , coupled cluster , valence (chemistry) , atomic physics , ionization , cluster (spacecraft) , chemistry , open shell , ionization energy , physics , ion , molecule , quantum mechanics , organic chemistry , computer science , programming language
An open‐shell coupled‐cluster method for the direct calculation of excitation energies is presented and applied to excitations of atomic Mg and Ar. The so‐called CCSD + T approximation involves the exact inclusion of T 1 and T 2 operators and the lowest‐order inclusion of T 3 . Quasi‐complete model spaces, built from determinants with one valence hole and one valence particle, are used. Two ionization potentials and 20 excitation energies are calculated. Good agreement with experiment (˜0.2 eV) is obtained. The T 3 effects are less important than for the Be and Ne atoms.