The coupled-cluster corrections to multi-reference configuration interaction method with singles and doubles (MR-CISD) are applied to describe the N-2 dissociation process which is a prototypical case of the triple-bond breaking. The exact solvability of the double-zeta N-2 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. (C) 2004 Elsevier B.V. All rights reserved.