A density functional study of thorium tetrahalides

The results of a study on the ground states of thorium tetrahalides using density functional theory are presented. The equilibrium geometries of ThX₄ (X = F, Cl, Br, I) have been optimized and their harmonic frequencies have been calculated. In the geometry optimizations the results were generated by using two different density functional programs, namely GAUSSIAN98 and MAGIC. Both local and non-local functionals were used. This allowed us to benchmark the MAGIC program and check the consistency of the theoretical predictions between different codes. Equilibrium structures, harmonic frequencies and zero-point energies were then calculated for a wider range of methods using GAUSSIAN98. Among these methods Hartree-Fock and Møller-Plesset second-order perturbation theory are included. All the calculated results are compared with experimental values where available. The frequencies of only the v₃ and v₄ vibrational modes have been measured for ThF₄ and only v₃ has been measured for ThCl₄, while no vibrational frequencies have been measured for ThBr₄ and ThI₄. It is thus important to obtain improved values for all the vibrational frequencies of these molecules. Comparison can then be made with existing values, most of which have been derived from empirical correlations with results from related lighter tetrahalide molecules.