APPROXIMATE BRUECKNER ORBITALS AND SHAKEUP OPERATORS IN ELECTRON PROPAGATOR CALCULATIONS - APPLICATIONS TO F- AND OH-

Vertical electron detachment energies of F- and OH- have presented dif ficulties for perturbative electron propagator methods. A recently der ived, nondiagonal, renormalized approximation and two additional impro vements are studied here. These improvements are replacement of the Ha rtree-Fock reference determinant by a determinant of approximate Bruec kner orbitals generated by a coupled-cluster doubles calculation and r etention of correlation terms in the 2hp-2hp block of the superoperato r Hamiltonian matrix. Agreement with experiment is significantly bette r with these methods. When Hartree-Fock orbitals are used, electron de tachment energies are underestimated, but approximate Brueckner orbita ls lead to overestimates. (C) 1998 John Wiley & Sons, Inc.