According to recent observations - 60 and calix[5]arenes (31,32,33,34,35-pentahydroxy calix[5]arene calix[5]arene: 1, and 5,11,17,23,29-pentamethyl- 31,32,33,34,35-pentahydroxy: 2) in two different crystal structures [1,2], a theoretical study was performed to analyze the electronic structure and interaction of this type of noncovalent complexes. The aim of this work is find out the suitable functionals to study on these host-guest complexes. The theoretical approach is first applied to calculation of interaction energies between two benzene molecules in T-shaped and parallel-displaced structures [3] using several density functionals. The geometries of benzene dimers in the gas-phase were fully optimized with SVP basis set at PBE, B1B95, B3LYP, B3PW91, B97-1, BP86, MPW1PW91, MPWB1K, MPW1B95, PW91, M05, M05-2X, M06, M06-2X as well as MP2 levels of theory using the Gaussian 09 set of programs. Among 14 tested functionals, the M06-2X gives the closest interaction energy values to the MP2. The result show that the M06-2X functional gives the maximum amount of calculated binding energy of C60 with calix[5]arene. In contrast, most of the other popular density functionals fail to describe this noncovalent interaction or yield purely repulsive interactions.
