Comparative study of spectroscopic properties of some indium , tin and antimony compounds

Spectroscopic properties of dimers, hydrides, oxides, fluorides and sulphides of the elements In, Sn and Sb have been calculated using energy-adjusted pseudopotentials. Results are given for bond lengths R e, dissociation energies D e, vibrational frequencies co e and dipole moments #e of the ground states. Comparison is made both with experimental and theoretical values, where available. The influence of core-core overlap, of valence correlation as well as of core-valence correlation is discussed. For In2, three low-lying states have been investigated. Contrary to experimental results, the ground state of In 2 is found to be 31-I. Ionization potentials of In, Sn, Sb and electron affinities of O, F, S have also been calculated. Theoretical investigations on molecules become rather rare with increasing atomic number of the elements because of the drastic increase of computational effort. This effort can be reduced by using pseudopotentials I-1-5]. Only the valence electrons are treated explicitly, while the core is represented by a pseudopotential. In addition, relativistic effects become more and more important with increasing atomic number. In contrast to relativistic all-electron calculations, which, for molecules , are mostly restricted to the Dirac-Fock (DF) level up to now (for a review see [6]), relativistic effects can be included into pseudopotentials in a simple way. Therefore, the pseudopotential method seems to be the most successful molecular theory for heavy atoms I-7]. Further merits of the pseudopotential method are that there is no significant loss in accuracy, and that all elements of the same group of the Periodic Table can be treated on equal footing. For the main group elements In, Sn and Sb, pseudopotentials have been published by several authors [8-14]. Instead of the adjustment to orbital energies and orbital densities [8-13], the pseudopotentials used in this work [14] are fitted to experimental ionization and excitation energies of one-valence electron atoms 1-15]. This treatment implicitly includes relativistic effects. Core-valence correlation can easily be introduced by means of an additional core-polarization potential 1,16] without extension both of the valence shell to d orbitals and of the basis set to f functions. Applications of our pseudopotentials to various main group element compounds have been published in the last few years 1,17-25]. Deviations from reliable experimental data are almost negligible for alkali compounds 1,18-20, 22] (ARe = 0.03 A and AD e = 0.02eV), but increase for hydrides and oxides 1,24] of fourth-row elements up to AR e = …