Abstract:A constant denominator perturbation theory based on a zeroth-order Harniltonian characterized by degenerate subsets of orbitals is developed to fourth order. This formulation allows a decoupling of the numerators of the perturbation sequence, allowing for a much more rapid evaluation of the resulting sums. Although the theory is general, a constant denominator is chosen as a scaled difference between the average occupied and average virtual orbital energies. The correction for this choice is folded back into t… Show more
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