TOTALLY DRESSED SDCI CALCULATIONS - AN APPLICATION TO HF AND F2

A previously proposed procedure including the linked and unlinked contributions due to Triple and Quadruple excitations into a size-consistent 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 total dressing model, which is based on the intermediate Hamiltonians theory. Three basis sets have been employed: the correlation consistent cc-pVTZ basis, a similar one including 3d1f polarization functions, and another including one set of g polarization functions. Excellent agreement with experiment and high-quality calculations is obtained for both equilibrium distances and spectroscopic constants. The possibilities of the method in treating single-bond breaking are also demonstrated. Finally, the Linked and Non-Linked contributions from Triple and Quadruple excitations are analysed separately and it is suggested that the addition of the linked triples to the size-consistent SDCI is sufficient to have quantitatively correct spectroscopic properties in going from the size-consistent SDCI to nearly experimental values.