MOLECULAR-ORBITAL DESCRIPTION OF CORE EXCITATION-SPECTRA IN TRANSITION-METAL COMPOUNDS - AN AB-INITIO CI CALCULATION ON TICL4 AND ISOELECTRONIC MOLECULES

Ab initio calculations of 1s and 2p core excitation spectra are performed in the relaxed 1h-1p CI scheme for a series of isoelectronic and isostructural halides and oxohalides (TiF4, TiCl4, TiBr4, VOF3, VOCl3, CrO2F2, CrO2Cl2, MnO3F, MnO3Cl). Agreement with experimental spectra available for TiCl4 is very satisfactory, indicating the reliability and accuracy of the present model to describe core excitation spectra even in highly ionic transition metal compounds. The calculated spectra show significant and well detectable variations upon halogen or metal substitution, and are therefore a sensitive probe to slight electronic structure changes along the series. Significant configuration mixing are observed among different excitation channels in the case of the degenerate 2p core hole, and prevent full account of the spectra in a pure one-electron model.