Generation of potential energy curves for the X1 Σ+g B1 Δ+g and B' 1Σ+g states of C2 using the effective valence shell Hamilionian method -: art. no. 154310

Calculations of the ground and excited state potential energy curves of C-2 using the third-order effective valence Hamiltonian (H-3rd(v)) method are benchmarked a ainst full configuration interaction and other correlated single-reference perturbative and nonperturbative theories. The large nonparallelity errors (NPEs) exhibited even by state-of-art coupled cluster calculations through perturbative triples indicate a serious deficiency of these sing] e-reference theories. Th H-v method, on the other hand, produces a much reduced NPE, rendering it a viable approximate many-body method for accurately determining global ground and excited state potential energy curves/surfaces. (c) 2005 American Institute of Physics.