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Application of the valence‐universal coupled‐cluster method based on various model spaces. II. Nonstandard solutions for Be
Author(s) -
Jankowski K.,
Malinowski P.
Publication year - 1996
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/(sici)1097-461x(1996)59:3<239::aid-qua7>3.0.co;2-z
Subject(s) - coupled cluster , basis set , valence (chemistry) , excited state , physics , nonlinear system , cluster (spacecraft) , basis (linear algebra) , space (punctuation) , atomic physics , mathematics , quantum mechanics , geometry , molecule , computer science , programming language , operating system
The impact of the choices of the complete model space (CMS) and of the orbital basis set on the existence, attainability, and properties of the nonstandard solutions of the valence‐universal coupled‐cluster (VU‐CC) methods has been studied for the case of nonlinear equations corresponding to the atomically oriented form of these methods accounting for one‐ and two‐electron excitations (VU‐CCSD/R method) and applied to the Be atom. The results for five 1 S states are discussed. In addition to the previously applied CMS defined by the orbital set (2 s, 2 p ) and (2 s, 3 s ), we have employed the CMSs defined by the (2 s, 2 p, 3 s ) set. For each of the CMSs several nonstandard solutions are documented. It is found that the energies of the individual states corresponding to standard and nonstandard solutions differ very little. These energies are also almost independent on the choice of CMS. On the other hand, the energies of excited states disclose a strong dependence on the radial structure of the orbital basis set. It is also demonstrated that the magnitudes of the cluster amplitudes representing a set of states depend both on the choice of the CMS and whether they correspond to the standard or nonstandard solutions. © 1996 John Wiley & Sons, Inc.