All calculations were performed with the open source NWChem software package vi by using Becke's three-parameter hybrid B3LYP functional, while the molecular orbitals are expanded in triple-zeta all electron 6-31 set with added polarization and diffuse functions ]. vii B3LYP functional has been proven to give accurate description of geometries, frequencies, relative stabilities of different conformers and the energy profile calculation, not only in previous literatures, viii but also in the benchmarking studies done previously using Gaussian 09 software.