Can ordinary single-reference coupled-cluster methods describe the potential energy curve of N2? The renormalized CCSDT(Q) study

The recently proposed renormalized and completely renormalized CCSDT(Q) methods, which result from the method of moments of coupled-cluster equations, have been implemented and applied to the potential energy curve of N2. It is shown that the renormalized and completely renormalized CCSDT(Q) methods, employing the restricted Hartree–Fock reference, provide very good description of the potential energy curve of N2, in spite of the failure of the full CCSDT and perturbative CCSDT(Qf) approaches at large N–N separations.