Abstract
The performance of the DFT/B-97-D and omega B97-D methods to reproduce the isotropic non-bonded interaction and the electric response properties in the benzene argon and the pi-pi interaction in the benzene dimer have been studied. The PES for the interaction of benzene and argon with all possible Ar-n-benzene (n = 1, 2) conformations has been explored. Results indicate that the omega B97-XD method is capable of reproducing well positions and depths for the studied benzene-Ar and benzene-benzene clusters to a high degree of accuracy and compare well with the experimental and best benchmark calculations. Satisfactory results have also been obtained for the benzene-X (X = He, Ne and Kr) clusters. The features of the charge density distributions of the studied benzene-Ar van der Waal complexes have been analyzed by calculating the dipole and higher multipole moments and the static polarizibility, its anistropic part and the interaction polarizibility. Trends and relationships to the dispersion interaction energy are suggested. Natural bond orbital analyses of the benzene-Ar-n vdw complexes show clearly that all carbon valence orbitals are over-populated by about 21% at the expense of the hydrogen atoms valence orbitals. These data also indicate that argon behaves as electron donor in the Ar-benzene vdw complex, and hence, the slight positive charge on argon is at on the expense of its valence (non-bonding) p-orbitals.