PROPERTIES OF MOLECULES CALCULATED FROM SCF WAVEFUNCTIONS

Three separate projects are presented. The first is an attempt to explain observed photo-isomerizations of acyclic azoalkanes. A set of simple models based on minimal basis set molecular wavefunctions calculated using an approximate SCF method (PRDDO) are formulated. The models are successful in their qualitative explanations of observations. In addition, more elaborate, ab-initio and MSCSF calculational results for some molecular geometries are presented. PRDDO results fare well in comparison.;The final project involves calculation of SCF wavefunctions for carboranes containing five or six heavy atoms. Some "classical" structures, i.e. structures involving only ordinary two-center bonds, are found to be very close in energy to the observed, non-classical configurations. The new structures are proposed as intermediates in rearrangement reactions.;The second project is introduced by presenting the results of an experiment involving elastic and inelastic scattering from water, methanol and a 50% (Vol.) mixture of the two. The initial stages of the development of a model capable of describing the elastic scattering results are reported. This involves the Fourier transformation of SCF-LCAO wavefunctions employing Slater-type basis functions. A tractable calculational method for performing the transformations is developed and some of the details of the computer implementation of the method are presented. An alternative to the free, spherical atoms model for use in the refinement of crystal structures is developed. The model is based on partitioning the electron density in the unit cell into spherically symmetric atomic cores and chemically invariant valence structures derived from localized molecular orbitals. Scattering factors for C-H and three types of C-C bonds, obtained by Fourier transforming "average" lmo's are presented. The lmo method is shown to produce more accurate atomic positional parameters than the free atoms model in mock refinements in which the "observed" structure factors are obtained by Fourier transformation of electron densities obtained from calculated wavefunctions.