Recent Progress in Coupled Cluster Methods. Theorey and Applications

0346316 - ÚFCH JH 2011 RIV NL eng M - Monography Chapter
Kedžuch, S. - Demel, Ondřej - Pittner, Jiří - Noga, J.
Multireference R12 coupled cluster theory.
Recent Progress in Coupled Cluster Methods. Theorey and Applications. 1. Dordrecht: Springer, 2010 - (Čársky, P.; Paldus, J.; Pittner, J.), s. 251-266. Challenges and Advances in Comput. Chem. Phys., 11. ISBN 978-90-481-2884-6
R&D Projects: GA ČR GA203/07/0070
Institutional research plan: CEZ:AV0Z40400503
Keywords : Hilbert space * multireference coupled cluster * R12 approach
Subject RIV: CF - Physical ; Theoretical Chemistry

In order to account for static electron correlation, the explicity correlated coupled cluster(CC) theory based on the R12 Ansatz is formulated with respect to a multi-determinantal reference using the Brillouin-Wigner (BW) approach. Though the latter avoids appearance of the intruder states, one pays for this desired feature by the loss of size extensivity. However, to some extent this can be remedied by an posteriori correction. Since the BW-CC method offers simples form of amplitude equations among Hilbert space MR CC ones, we have chosen it as the first step when developing MR CC-R12 approaches. It is shown that introducing of the basis set incompleteness correction via an explicit inclusion of the correlation factor into the wave function, separately for each reference, is easily realizable. Test calculations for the H4 model using the R12 optimized 9s6p4d3f basis and its subsets with increasing highest angular momentum show the potential of the MR CC-R12 approach.
Permanent Link: http://hdl.handle.net/11104/0187382