“…41,66,80,81,92,93 It is generally accepted that the MP2/ DZP theory can also give reasonable accuracy; however, quite surprisingly, we found that overall the performance of the B3LYP/6-31G(d,p) in internal coordinate is even better than the MP2/DZP combination in Cartesian coordinates. It is believed that the B3LYP/ 6-31G(d,p) potential in the internal coordinate works better in predicting vibrational frequencies, 40,83 which is in agreement with our results here. However, we also calculated the fundamental frequencies of the three molecules using the VSCF method in Cartesian coordinates in combination with the B3LYP/6-31G(d,p) potential, the RMSD of which are found to be 25-45 cm À1 more than that of the case using the internal coordinate with the same theory and basis set (data not shown).…”