Multi-reference configuration interaction , performance

Multi-Reference Configuration Interaction (MRCI) calculations were subsequently performed on the saddle point, the reagents, and the products, in order to improve the determination of the barrier height and the exoergicity. These calculations, which include single and double excitations from the active orbitals, have been performed by using the direct-CI method [10]. Davidson s correction [11] was also added to account for the effect of unlinked clusters this will be denoted MRCI-I-Q in Table 1. 

A posteriori corrections can be developed for calculations performed by using the Brillouin-Wigner perturbation expansion. These a posteriori corrections can be obtained for the Brillouin-Wigner perturbation theory itself and, more importantly, for methods, such as limited configuration interaction or multi-reference coupled cluster theory, which can be formulated within the framework of a Brillouin-Wigner perturbation expansion. 

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