Atom-type assignment in molecules and clusters by perturbation theory-A complement to X-ray structure analysis.

An approach to distinguish elements with similar atomic numbers in molecules and clusters is presented and applied to experimentally synthesized and structurally characterized mixed-metallic compounds. By first treating a homogenized reference system constructed from the original compound and applying first-order perturbation theory it is possible to find the most stable distribution of the atom types to the atomic sites in a very efficient way. This work is focused on the appropriate choice of homogenized reference systems and on applications treating experimentally synthesized compounds. With these examples is shown that the method is a helpful complement to X-ray crystal structure analysis.