Cluster analysis and pair function synthesis of correlated wavefunctions.

The problem of electron correlation in the field of atomic and molecular structure calculations is briefly reviewed. Various highly accurate atomic wavefunctions obtained from the literature have been analysed into the cluster form given by Sinano?lu and the orbital correction and pair correlation functions so obtained have been examined in detail. Computer programs have been developed to apply the method of Sinano?lu's Many Electron Theory to determine closed shell atomic and molecular wavefunctions in terms of Hartree-Fock orbitals and pair correlation functions. Various special techniques have been employed in the determination of the pair functions. These programs have been used to synthesise a series of wavefunctions for the Be-like ions and we have examined the effect on a number of one-particle expectation values of including only selected pair correlation interactions within the wavefunctions. In addition, we have investigated the effect of correlation on the 1S-1P generalised oscillator strength for the Be-like ions, the 1S-1P inelastic scattering cross-sections for electron and proton impact on beryllium and also on the photoionisation cross-section (or continuous oscillator strength) for both the He-like and Be-like ions. Approximate molecular pair correlation energies have been obtained for a series of diatomic hydrides and the variation of these quantities with bond distance has been discussed. Finally, we have determined spectroscopic constants for these molecules from the uncorrelated potential curves and also from potential curves obtained by representing the total correlation energy as the sum of our individual molecular pair energies.