A method for analysis of separate sigma and pi overlap populations in a system of very low symmetry has been proposed. The calculations are performed in Ti3O3, rutile, anatase, brookite and tetragonal barium titanate. The examination of the various bond overlap populations has led to reasonable explanation on the infrared absorption spectra of CO and CO3 chemisorption on rutile and anatase and the relative heats of formation of anatase, rutile and brookite.
Extended Huckel molecular orbital calculations have been performed on localized TiOs8-units with the precise geometry of such a unit in solid rutile, anatase, and brookite TiO, and tetragonal BaTi03. The relative values of one-electron energy levels in these conlpounds are obtained in terms of a "self-consistent" charge and population calculation. Examination of the resulting energy levels and charge distributions has led to reasonable explanations of previously unexplained data on (1) the visible and near-ultraviolet absorption spectra of these compounds, (2) the low energy X-ray absorption edges of rutile, anatase, and brookite TiO,, and (3) the pressure dependence of the absorption edges of rutile TiO, and tetragonal BaTiO,.Canadian Journal of Chemistry, 46, 2667Chemistry, 46, (1968
IntroductionThe extended Hiickel molecular orbital (m.0.) theory applied to transition metal compounds has been carried out for various ions and compounds (1-12). Although the initial results are encouraging, it is clear that there is a need for a standard and consistent method of choosing the parameters in the calculation which can be transferred from one transition metal compound to another. It also seems desirable to explore whether this method can explain other phenomena besides the normal absorption spectra. Since the structures and optical data of rutile, anatase, and brookite TiO, and BaTiO, are available (13-26), it is of interest to examine these compounds by performing molecular orbital calculations on hypothetical localized Ti068-units with the exact geometries of the units in the parent compounds.
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