VESCF-MO studies of molecules containing atoms from the second row of the Periodic Table. I. The general problem

As a preliminary step in the development of a satisfactory molecular-orbital treatment of molecules incorporating second-row atoms, the VESCF molecular-orbital method is reconsidered, particularly with respect to evaluation of basic parameters. Appropriate methods of deriving valence-state ionization potentials, resonance integrals, monocentric and bicentric coulomb repulsion integrals, and monocentric exchange integrals are considered. The particular problem of properly treating 3d-orbitals is examined and the use of Burns's rules for evaluating orbital exponents is suggested. Since the efficacy of the various procedures depends upon obtaining reliable molecular wave functions, a brief review is given of the kinds of experimental data that will be used in Part 11 to test the VESCB wave functions.