Renormalized CCSD(T) and CCSD(TQ) approaches: Dissociation of the N-2 triple bond

The recently proposed renormalized and completely renormalized CCSD(T) and CCSD(TQ) methods, which can be viewed as generalizations of the noniterativ e perturbative CCSD(T) and CCSD(TQ(f)) schemes and which result from the mo re general method of moments of coupled-cluster equations, are applied to t he dissociation of the ground-state N-2 molecule. It is shown that the reno rmalized and completely renormalized CCSD(T) and CCSD(TQ) methods provide s ignificantly better results for large N-N separations than their unrenormal ized CCSD(T) and CCSD(TQ(f)) counterparts. (C) 2000 American Institute of P hysics. [S0021-9606(00)30538-4].