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Ground states of BeC and MgC: A comparative multireference Brillouin–Wigner coupled cluster and configuration interaction study
Author(s) -
Teberekidis Vasilios I.,
Kerkines Ioannis S. K.,
Tsipis Constantinos A.,
Čársky Petr,
Mavridis Aristides
Publication year - 2004
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.20379
Subject(s) - multireference configuration interaction , coupled cluster , basis set , chemistry , atomic physics , ground state , full configuration interaction , computational chemistry , configuration interaction , physics , molecule , density functional theory , organic chemistry
The competing X 3 Σ − and 5 Σ − states of the experimentally unknown alkaline–earth metal carbides BeC and MgC are examined with the multireference Brillouin–Wigner coupled cluster method restricted to single and double excitations (MRBW‐CCSD). The results are compared against the traditional single‐reference CCSD approach, as well as with other single and multireference methods. In both molecules, the CCSD 5 Σ − ← X 3 Σ − energy difference is underestimated, leading to an “erroneous” ground‐state prediction in BeC. The MRBW‐CCSD method corrects this anomalous behavior, leading to fair agreement with multireference configuration interaction (MR‐CI) predictions. Our results at the highest levels of theory are extrapolated to the basis set limit, and the core/valence correlation is taken into account, leading to very accurate energetics and spectroscopic constants in both carbides. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005