Approximate Brueckner orbitals in electron propagator calculations

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