Generalizing the bra state in the symmetry-adapted cluster singles and doubles method and the second-order perturbation correction

Autor:	Jun-ya Hasegawa, Akihiro Obata, Kenji Matsuda
Rok vydání:	2010
Předmět:	Physics Classical mechanics Present method Potential curves General Physics and Astronomy Perturbation (astronomy) Physical and Theoretical Chemistry Mathematical physics
Zdroj:	Chemical Physics Letters. 486:84-88
ISSN:	0009-2614
DOI:	10.1016/j.cplett.2009.12.080
Popis:	We present a procedure to overcome the quasi-degeneracy problem in the CCSD and SACSD methods. A multi-configuration bra state in the SACSD equations (MRbra-SACSD equation) together with a second-order perturbation correction gives quantitatively correct potential curves for bond dissociations. The benchmark results for HF, F 2 , and H 2 O show that the perturbative triple correction reduces the deviations from Full-CI energies to within 3 mHartree (1.9 kcal/mol). Within the benchmark calculations, the results of the present method are comparable with the recent post-CCSD corrections, the CR-CCSD(T) and CCSD(2) T methods, and are slightly less accurate than the CR-CC(2,3) method.
Databáze:	OpenAIRE
Externí odkaz:	https://explore.openaire.eu/search/publication?articleId=doi_dedup___::42e8d40ee7cfb388e097f2bdd3080d03 https://doi.org/10.1016/j.cplett.2009.12.080 Zobrazit plný text záznamu Full Text from ScienceDirect