SEMIEMPIRICAL AND AB-INITIO CALCULATIONS OF DIATOMIC HETERONUCLEAR MOLECULES DOPED INTO CUBIC-CRYSTALS - COMPARISON TO EXPERIMENTAL-DATA

The optical spectra of diatomic molecules AB, A = Sn, Pb; B = S, Se, T e doped into KCL and KBr are quite different from data of the isolated species. From semi-empirical calculations shifts of electronic bands of the free AB compared to the doped molecules are obtained. The HOMO- LUMO gap is increased when the molecule AB is surrounded by host atoms . A tentative assignment is made for the lowest electronic transitions . Ab-initio methods allow for the calculation of vibrational frequenci es of free molecules and the dopants as well. Starting from AB, neighb ours on the A-B axis and at least one shell of host atoms is added. Th e results are used to assign experimental data.