Approximate Brueckner orbitals in electron propagator calculations

Orbitals and ground-state correlation amplitudes from the so-called Brueckn er doubles approximation of coupled-cluster theory provide a useful referen ce state for electron propagator calculations, An operator manifold with ho le, particle, two-hole-one-particle and two-particle-one-hole components is chosen. The resulting approximate propagator may be regarded as an extensi on of the 2ph-Tamm-Dancoff approximation, third-order algebraic diagrammati c construction [2ph-TDA, ADC (3)] and 3+ methods. The enhanced versatility of this approximation is demonstrated through calculations on valence ioniz ation energies, core ionization energies, electron detachment energies of a nions, and on a molecule with partial biradical character, ozone. (C) 1999 John Wiley & Sons, Inc.