Ab initio calculations for small iodo clusters. Good performance of relativistic effective core potentials

Abstract

The iodine clusters I 2( 1Σ g +), I 2( 3Π u), I 2 −( 2Σ u +) and I 3 −( 1Σ g +), as well as excited states of I 2 −( 2Σ u +) and I 3 −Σ g +), have been examined by means of different ab initio methods ranging from the SCF-HF to the QCISD(T) theoretical levels coupled with the relativistic effective core potential approach in a non-relativistic symmetry. The QCISD(T) method, with valence basis sets augmented by two sets of d polarization functions, was found to be reliable. The calculated equilibrium bond lengths, harmonic frequencies, force constants, bond dissociation energies, electronic transition energies and electron affinities are in good agreement with experimental data.