AB-INITIO CALCULATIONS FOR SMALL IODO CLUSTERS - GOOD PERFORMANCE OF RELATIVISTIC EFFECTIVE CORE POTENTIALS

The iodine clusters I-2((1) Sigma(g)(+)), I-2((3) Pi(u)), I-2(-)((2) S igma(2)(+)Z(u)(+)) and I-3(-)((1) Sigma(g)(+)), as well as excited sta tes of I-2(-)((2) Sigma(u)(+)) and I-3(-)((1) Sigma(g)(+)) have been e xamined by means of different ab initio methods ranging from the SCF-H F to the QCISD(T) theoretical levels coupled with the relativistic eff ective core potential approach in a non-relativistic symmetry. The QCI SD(T) method, with valence basis sets augmented by two sets of d polar ization functions, was found to be reliable. The calculated equilibriu m bond lengths, harmonic frequencies, force constants, bond dissociati on energies, electronic transition energies and electron affinities ar e in good agreement with experimental data.