Abstract
A method is suggested which allows the inclusion of dynamic correlation into CASSCF calculations. An effective Coulomb hole potential is added to the Hamiltonian. The potential has a simple form, which allows its implementation into existing LCAO programs using Gaussian integral packages. The parameters appearing in the potential are determined by fitting to empirical valence correlation energies for first row atoms. Calculations of ionization energies and electron affinities show considerable improvement compared to the MCSCF values. Test calculations on three molecules give the following results, H2∶ re=0.745 (0.741) A, De=4.62 (4.75) eV; N2∶ re=1.099 (1.098) A, De= 10.42 (9.91) eV; O2∶ re=1.198 (1.207) A, De=4.73 (5.21) eV. Experimental values within parenthesis.
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