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A study of quasidegeneracy effects in the be‐isoelectronic series
Author(s) -
Adams B. G.,
Jankowski K.
Publication year - 2009
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.560240834
Subject(s) - excited state , series (stratigraphy) , wave function , ion , atomic physics , perturbation theory (quantum mechanics) , configuration interaction , chemistry , perturbation (astronomy) , effective nuclear charge , physics , quantum mechanics , paleontology , biology
Coupled‐pair (CPMET), doubly‐excited configuration interaction (D‐CI) and linear coupled‐pair (LCPMET) calculations on several members (Li − , Be, B + , C 2+ , Ne 6+ , Ar 14+ , Zn 26+ ) of the Be‐isoelectronic series are reported and compared with other methods such as perturbation theory. Special attention is given to the reliability of coupled‐pair methods for both positive and negative ions in the presence of quasidegeneracy. The impact of disconnected quadruply excited configurations is significant for Li − and decreases considerably for the positive ions as the nuclear charge increases. The present single‐reference state results indicate that coupled‐pair methods are considerably more accurate than perturbation theory in the quasidegenerate systems considered. It is also emphasized that the description of quasidegeneracy effects should take into account both the energies of the configurations involved and the relative magnitudes of these configurations in the wave function.