ADVANTAGES AND DRAWBACKS OF THE QUANTUM-CHEMISTRY METHODOLOGY IN PREDICTING THE THERMOCHEMICAL DATA OF LANTHANIDE TRIHALIDE MOLECULES

DFT calculations have been carried out on six lanthanide trihalide mol ecules, using Stuttgart ECPs on the lanthanides and a 6-31G all-elect rons basis set on the halogens. These calculations have been compared to previous theoretical and experimental data. Calculated bond lengths and vibrational frequencies are found to be in good agreement with pr evious theoretical results. The variations observed between experiment al and theoretical results are discussed. Therefore, thermochemical da ta have been derived from such calculations. In this paper, the advant ages and drawbacks of this methodology are discussed in the framework of the selected heavy elements. The different factors which influence the estimated thermochemical data have been compared. While molecular parameters seem to have a weak influence on the thermochemical functio ns, low frequencies (flat energy surfaces along the out-of-plane disto rtion) and the electronic partition function have been revealed to be the main factors for the accuracy of the predicted thermochemical data . (C) 1998 Elsevier Science S.A.