Breaking N2 triple bond: the coupled-cluster corrected multi-reference configuration interaction description

The coupled-cluster corrections to multi-reference configuration interaction method with singles and doubles (MR-CISD) are applied to describe the N2 dissociation process which is a prototypical case of the triple-bond breaking. The exact solvability of the double-zeta N2 model used in the calculation permits comparison of results obtained within approximate schemes with the exact ones thus allows us to evaluate their performance. In our approach the MR-CISD method is corrected to improve description of the dynamic correlation thus an adequate selection of the MR-CISD reference space becomes an important factor for the successful application of the method. Several different reference spaces are tested.