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General-model-space many-body perturbation theory: The (2s3p)/sup 1,3/P states in the Be isoelectronic sequence

Journal Article · · Phys. Rev. A; (United States)
The energies of the (2s3p) /sup 1,3/P states of the Be sequence ions N IV--Ne VII are calculated, with use of a general-model-space many-body perturbation theory (MBPT) to third order. The triplet states are described accurately by a one-configuration model (P) space including only 2s3p, but the singlets are not; the singlet-triplet separation has the right sign (singlet below triplet) but is only 30% of experiment. Incorporation of the 2p3s configuration in the model space greatly improves the results. This incomplete, two-configuration model space yields virtually the same energies as the larger, complete model space required by other quasidegenerate MBPT methods, at one-fifth the computational cost.
Research Organization:
Chemistry Department, Tel-Aviv University, Tel-Aviv 69978, Israel
OSTI ID:
6265206
Journal Information:
Phys. Rev. A; (United States), Journal Name: Phys. Rev. A; (United States) Vol. 30:6; ISSN PLRAA
Country of Publication:
United States
Language:
English