Determination of atomic partial charges using X-ray photoelectron spectroscopy: application to crystalline solids

Abstract

The direct calculation, for a crystal of any structure, of atomic partial charges from XPS core level chemical shifts is described. The effects of the infinite crystal lattice are accounted for systematically. The equation for each chemical shift is taken as linear in the atomic partial charges, with the same approximations as in previous calculations. The validity of this approach is examined using molecular orbital theory and another linear equation, less approximate than the above, is obtained. Atomic partial charges are calculated for four crystalline oxides of lead, using both the above equations in turn. The Fermi energy for each compound is also obtained. The atomic partial charges associated with the two oxidation states of lead in the Pb₃O₄ crystal are found to differ considerably although, in the XPS data used in the calculation, both these states exhibit the same chemical shift. The inclusion of lattice effects in the calculation is responsible for this result.