Theoretical investigations for the molecular structures and binding energies for C6H6(H2O)n, (n=1-7) complexes

The geometrical parameters, vibrational frequencies, and dissociation energies for (H2O)(n) and C6H6(H2O)(n) (n=1-7) clusters have been investigated using density functional theory (DFT) with various basis sets. The highest levels of theory employed are B3LYP/aug-cc-pVTZ for optimization and MP2/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ for binding energy. The harmonic vibrational frequencies and IR intensities are also determined at the various levels of theory to confirm whether the hydrogen-bonded structure of water complex (W-n, n = 1-7) is affected by the presence of benzene. The effect of benzene on the OH stretch modes of benzene-water complex (BWn, n = 1-7) is observed in the pi-hydrogen bonded OH stretch. For each of the BWn clusters the intensity of this mode is increased significantly due to charge transfer/polarization interactions and the frequency shifts from Wn to BWn are in the range of 40-60 cm(-1). The calculations give the binding energies of 2.58, 4.20, 3.27, 3.00, 3.42, 4.14, and 5.49 kcal/mol for BW1-BW7, respectively after ZPVE and 50%-BSSE corrections.