TOTALLY DRESSED SDCI CALCULATIONS - AN APPLICATION TO HF AND F2

A previously proposed procedure including the linked and unlinked cont ributions due to Triple and Quadruple excitations into a size-consiste nt SDCI-like model has been applied to HF and F-2 single-bond systems. The procedure is a non-iterative approximation to the more general to tal dressing model, which is based on the intermediate Hamiltonians th eory. Three basis sets have been employed: the correlation consistent cc-pVTZ basis, a similar one including 3d1f polarization functions, an d another including one set of g polarization functions. Excellent agr eement with experiment and high-quality calculations is obtained for b oth equilibrium distances and spectroscopic constants. The possibiliti es of the method in treating single-bond breaking are also demonstrate d. Finally, the Linked and Non-Linked contributions from Triple and Qu adruple excitations are analysed separately and it is suggested that t he addition of the linked triples to the size-consistent SDCI is suffi cient to have quantitatively correct spectroscopic properties in going from the size-consistent SDCI to nearly experimental values.