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 T1 and T2 operators and the lowest‐order inclusion of T3. 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 T3 effects are less important than for the Be and Ne atoms.
|Number of pages||9|
|Journal||International Journal of Quantum Chemistry|
|Issue number||20 S|
|State||Published - 1986|