Evaluation of Two Computational Models Based on Different Effective Core Potentials for Use in Organocesium Chemistry.

The performance of two computational models was evaluated in describing some aggregated structures, the bond lengths and dimerization energies of cesium halides, aquation energies of the cesium cation, and protonation energies of a range of organocesium compounds. One model used the Hay-Wadt (HW) effective core potential (ECP) and a double-ζ valence basis set on Cs; the other used the Ross ECP with two polarization functions on Cs. In both models, the standard 6-31+G** basis was used for the other atoms. At the Hartree-Fock (HF) level, the Ross ECP was found to give geometries and energies in good agreement with experimental results. Second-order Møller-Plesset calculations with this model gave only modestly improved results compared to HF; the B3LYP level gave variable results with unsatisfactory energies. Although the HW model is generally less satisfactory, it often shows comparable trends to those of the Ross model.