Non-empirical pseudopotentials for molecular calculations

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Abstract
The ability of the atomic pseudopotential proposed in Part I to reproduce the all-electron basis set extension and correlation effects in molecules has been tested on F2 and Cl2 through systematic comparisons between pseudopotential and all-electron calculations, at the SCF and CI levels, using three basis sets. The pseudopotentials monoelectronic energy levels, bond lengths and force constants have a perfect basis set dependence. The coefficients of the excited determinants in the ground-state wave-function resulting from limited CI's are in surprisingly high agreement, and the pseudopotential calculation reproduces very well the correlation effects on bond lengths and force constants, despite a 10 per cent overestimate of the total correlation energy. Pseudopotential extended (double-zeta+d) basis set calculations, including CI, have been performed on Br2 and I2, giving for I2 a better mean agreement with experiment than the presently available best all-electron calculations. The calculated dissociation energies fairly reproduce the experimental ordering (Cl2>Br2>I2>F2).