The performance of the multireference Brillouin-Wigner coupled cluster singles and doubles method on the insertion of Be into H2

The perpendicular (C(2v)) insertion pathway of (X(1)S) Be into (X(1)Sigma(g)(+)) H(2) is calculated by means of the multireference Brillouin-Wigner coupled cluster singles and doubles (MRBWCCSD) method and compared with the results of full configuration interaction (FCI), the multireference averaged coupled pair functional (MRACPF), and with previously reported MRCCSD results. MRBWCCSD is shown to provide a fairly accurate description of the BeH(2) potential energy surface. If higher accuracy is required, inclusion of connected triples into the MRCC model seems to be unavoidable. (C) 2004 Published by Elsevier B.V.