Approximations in the theoretical interpretation of Mössbauer spectra

An account is given how semiempirical molecular orbital calculations and accurate relativistic atomic calculations can be utilized to understand Mössbauer spectra of the heavy main-group elements Sn, Sb, Te and I. The various approximations are described and it is shown in which way experimental and semiempirical theoretical information can be combined consistently to gain insight into the electronic structure of the respective compounds. A set of qualitative correlations between calculated valence orbital occupations, effective charges, coordination numbers and measured isomer shifts is derived and the limited applicability of phenomonological models is elucidated.