Second row homopolar diatomic molecules. Potential curves, spectroscopic constants, and dissociation energies at the basis set limit for SCF and limited CI wave functions

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Abstract
Single configuration SCF calculations near the HF limit and CI calculations have been performed for the ground and selected excited states of the molecules Al+2 , Al2, Si+2 , Si2, P+2 , P2, S+2 , S2, Cl+2 , and Cl2. The CI calculation includes single and interacting double excitations from the valence orbitals of the single HF configuration. Potential energy curves from HF and CI wave functions, and with corrections for quadruple excitations, have been obtained for regions near the equilibrium bond lengths. Equilibrium bond lengths and vibrational separations for v=0–3 are calculated from these curves. Calculated ionization potentials are reported. Dissociation energies are calculated by determining the energies of the separated fragments in separate atomic calculations at the same level as the molecular calculations. The calculations are critically evaluated with emphasis on obtaining guide lines for more accurate work.