Modeling polymerization reactions at aluminum-based catalysts: Is DFT a reliable computational tool?

A large number of DFT approaches, including classical GGA approximations, h ybrid HF/DFT approaches, and more recent tau -dependent functionals, have b een tested for olefin polymerization reactions at a cationic aluminum syste m, and their results have been compared with refined post-HF methods. The r esults show that hybrid density functional methods always outperform classi cal GGA approaches, and more recent tau -dependent functionals are not yet competitive, providing nonsystematic errors in the energy evaluations. The effect of the lengthening of the polymer chain from the "standard" ethyl gr oup to a butyl group was found to be significant and hence has to be taken into account when predicting the molecular weight of polymers. A computatio nal strategy to study olefin polymerization at Al systems is proposed.