Theoretical Insight into the Interactions of TMA-Benzene and TMA-Pyrrole with B3LYP Density-Functional Theory (DFT) and ab Initio Second Order Møller−Plesset Perturbation Theory (MP2) Calculations

A detailed theoretical investigation of the tetramethylammonium(TMA)-benzene and TMA-pyrrole complexes has been performed to obtain the interaction properties of TMA with aromatics. Diffuse functions have been found to be important in the computational studies of these noncovalent complexes. Adding diffuse functions to the basis set decreases the binding energy by about 10% for the TMA-aromatic systems. Dispersion interactions in the TMA-aromatic systems are very important. They enhance the binding interactions between the TMA and the aromatic ring systems by about 0.5 kcal·mol-1 per interacting atomic pair, which is in agreement with the estimates of Rappe and Bernstein.1 Also, for the TMA-pyrrole complex, the presence of the dispersion interaction leads to a dramatic change in the optimized structure. Because B3LYP cannot handle properly the dispersion in the calculation, use of the Moller−Plesset second-order perturbation or other sophisticated methods should be considered in computational studies of c...