Of particular interest is the significant difference between ∆∆G ‡ 45 (∼ 0.010 kJ/mol) and ∆∆G ‡ 54 (∼ -0.464 kJ/mol), suggesting that the transition from the state 5 to 4 readily occurs in the DPMD model. This difference is likely arises from the involvement of many-body interactions, which plays a significant role when the bifurcated hydrogen bond exists. In contrast, ∆∆G 34 and ∆∆G 43 are similar.