As far as computational technique is considered, many practices have ascertained that DFT, which takes into account the exchange and correlation effects effectively, is most likely one of the best methods to study medium-size or larger molecular systems and appropriate for QSAR study, with exhibiting excellent performance than semiempirical method or some other ab initio methods. Complete geometry optimization for data set compounds was carried out using DFT with Becke's three-parameter exchange potential and the Lee-Yang-Parr correlation functional (B3LYP), using basis set 6-31G* level [90] . A useful kind of net atomic charges, called electrostatic potential (ESP)-fitting charges, were derived from the DFT calculated molecular electrostatic potential distribution using CHelpG method, which produces charges fit to the electrostatic potential at points selected. Vibrational frequencies were computed at the same B3LYP/6-31G* level to characterize the stationary points on the corresponding potential energy surfaces. All calculations were performed using the Gaussian 03 suite of programs.