Herbert E. Popkie

Molecular calculations with the MODPOT, VRDDO, and MODPOT/VRDDO procedures. II. Cyclopentadiene, benzene, diazoles, diazines, and benzonitrile

A procedure for carrying out nonempirical LCAO–MO–SCF calculations on large molecules is outlined. Use is made of an approximation for neglecting some one‐ and two‐electron integrals proposed by Wilhite and Euwema. The differential overlap between a pair of basis functions is set to zero if the pseudo‐overlap is less than the adjustable threshold. We refer to this method as variable retention of diatomic differential overlap (VRDDO). In addition, only the valence electrons may be explicitly considered. The influence of the core electrons is taken into account by using the model potential (MODPOT) Hamiltonian suggested by Bonifacic and Huzinaga. The two methods can be used together resulting in the MODPOT/VRDDO procedure. VRDDO, MODPOT, and MODPOT/VRDDO calculations are reported for cyclopentadiene, benzene, pyrazole, imidazole, pyridazine, pyrimidine, pyrazine, and benzonitrile. The accuracy of the VRDDO calculations is very good. Orbital energies and gross atomic populations differ from the reference val...

Molecular calculations with the VRDDO, MODPOT and MODPOT/VRDDO procedures. MODPOT/SCF + CI calculations to determine electron affinities of alkali metal atoms

Abstract Self-consistent field model potential (MODPOT/SCF) and model potential configuration interaction (MODPOT/CI) calculations have been carried out on the Li, Na and K atoms and on the Li − , Na − and K − anions. Only the valence electrons were considered explicity. The effect of the core electrons was taken into account by the use of a model potential (MODPOT) hamiltonian of the form similar to that proposed by Bonifacic and Huzinaga except that in this case we do not use a screened nuclear attraction term that is a function of the distance from the nucleus. We assume, instead, that the core electrons completely screen the atomic nucleus under consideration, thereby reducing the nuclear charge seen by the valence electrons from Z to Z - n C . The electron affinities were computed as the difference in calculated total energies between M − and M. Our calculated MODPOT/CI values are in excellent agreement with the exeperimental electron affinities. The results indicate that the MODPOT/CI method shows considerable promise for being able to calculate accurately the electron affinities of species containing medium and heavy atoms.