Atomic basis sets equivalent to the standard STO-3G and STO-6G ones were optimized for the elements of the first row using the generalized simulated annealing (GSA) approach. The atomic energies obtained with the new basis sets are substantially better than the ones obtained with the standard ones. The new basis sets were tested for several diatomic and triatomic molecules, at different levels of calculation. For the molecules at their geometries of equilibrium, the energies obtained with the GSA optimized basis are in general much better than the respective ones obtained with the standard basis. However, for molecules containing hydrogen atoms, the best results, either at the HF or CI level of calculation, are obtained with a combination of the new and the standard bases, which depend on the nature of the other atoms of the molecule. The analysis of the potential energy surfaces for the LiH, BH, and FH molecules showed that the new basis provide a better description of these molecules in all regions of the respective surfaces, although the equilibrium bond distances. The results are quite encouraging and clearly indicate that basis set of DZ and TZ quality better than the standard ones can probably be generated by the GSA approach.

In this work, we report a theoretical study on electron collisions with OH radicals in the low and intermediate energy ranges. Calculated elastic differential, integral, and momentum-transfer cross sections as well as grand-total (elastic + inelastic) and total absorption cross sections for electron-OH collisions are reported in the 1-500-eV range. A complex optical potential composed by static, exchange, correlation-polarization plus absorption contributions, derived from a fully molecular wave function, is used to describe the interaction dynamics. The Schwinger variational iterative method combined with the distorted-wave approximation is applied to calculate scattering amplitudes. Present calculated results are compared with the existing data for electron-OH scattering in the literature. Also, comparison made between our calculated cross sections for elastic scattering with the theoretical and experimental results for electron-H 2 O collisions has revealed remarkable similarity even at incident energies as low as 2 eV.

We present a theoretical study of electron collisions on SiH and SiF free radicals in the low-and intermediate-energy range. More specifically, calculated elastic differential, integral and momentum transfer cross sections as well as grand total ͑elastic and inelastic͒ and absorption cross sections are reported in the ͑1-500͒-eV energy range. A complex optical potential is used to represent the electron-radical interaction while the Schwinger variational iterative method combined with the distorted-wave approximation is used to solve the scattering equations. Comparisons were made between the calculated cross sections for SiH and SiF as well as with the existing experimental and theoretical data for electron scattering by silane molecule. Some interesting aspects of this comparison are discussed here.

In this work, we present a theoretical study on electron-methylidyne collisions in the low and intermediate energy range. More specifically, calculated elastic differential, integral and momentum transfer cross sections as well as grand total (elastic + inelastic) and absorption cross sections are reported in the 1-500 eV energy range. A complex optical potential is used to represent the electron-molecule interaction dynamics in the present calculation while the Schwinger variational iterative method combined with the distorted-wave approximation is used to solve the scattering equations. Comparison between the present absorption cross sections with the existing experimental and theoretical data for electron-impact ionization processes is encouraging.

ABSTRACT:The recently introduced multireference Hartree-Fock configuration interaction (MRHFCI) method has been applied to the calculation of the dipole moment of the LiH, BH, FH, CO, and H 2 O molecules. The results obtained indicate that MRHFCI wave functions, much more compact but of the same quality of the orthogonal full CI ones, can provide better dipole moments than the corresponding full CI wave functions. The value of the dipole moments obtained with the MRHFCI wave functions is quite insensitive to the choice of the HF references but the same is not true for the electronic energy. Therefore, further studies are necessary to develop a criterion for selecting a set of HF references which could provide the best values of energy and dipole moment. Also, it would be important to verify if other one-electron properties can be computed with the same degree of accuracy obtained for the dipole moments.