Efficient bond function basis set for pi-pi interaction energies.

Systematic study has been carried out to investigate the accuracy of mid-bond functions in describing pi-pi interactions in benzene dimer. Potential energy curves are calculated for the sandwich, T-shaped, and parallel-displaced configurations of benzene dimer by adding bond functions in MP2 (second-order Møller-Plesset perturbation theory) calculations with a wide range of split-valence and augmented, correlation-consistent basis sizes. At MP2 level, the largest basis set used with a bond function (denoted aug-cc-pVDZf-6s6p4d2f) differs by only approximately 0.1 kcal/mol relative to the result obtained from the standard aug-cc-pVQZ basis calculation (without the bond function). The calculated potential energy curves from the bond function basis aug-cc-pVDZf-6s6p4d2f and the larger standard basis aug-cc-pVTZ are in excellent agreement with each other for all three configurations. The number of bond function basis aug-cc-pVDZf-6s6p4d2f is 526 compared to 828 of aug-cc-pVTZ and 1512 of aug-cc-pVQZ. Current study shows that bond functions can be effectively employed to give accurate description of pi-pi interactions with the addition of only a minimal number of bond functions.