The parallel π-π stacking:: a model study with MP2 and DFT methods

The parallel pi-pi stacking of benzene molecules was studied using Density Functional Theory (DFT) and second-order Moller-Plesset perturbation theory (MP2) methods. The DFT methods are proved to be inadequate in prediction of pi-pi stacking conformation and interaction energy. Cluster model calculations at the MP2/6-311 + G** level predicted an optimized conformation which is very close to the structure of the parallel-displaced benzene dimer. The calculated inter-plane distance of 3.3 Angstrom is in good agreement with the observation in organic molecular crystals. The interaction energy predicted at MP2 level revealed that the pair-wise interaction energy increases with the number of the parallel-stacked benzene molecules. (C) 2004 Elsevier B.V. All rights reserved.