Semiempirical molecular orbital calculations: The ionization potentials of HgI 2 , the orbitals of the heavier elements, and the approximation of electron repulsion integrals

Calculations of the ionization potentials of HgI 2 using the ARCANA computer program and atomic data from Hartree‐Fock‐Slater (HSF) calculations reasonably approximate the experimental values without the incorporation of experimentally derived molecular parameters. Inclusion of the occupied 5 d shell of Hg and the empty 6 s of I reveals the inadequacy of the practice, widely employed in several semiempirical procedures, of using the same electron repulsion integrals for dissimilar orbitals on the same atom. HSF calculations provide a convenient unified source of atomic orbital data for the less familiar elements.