TABLE 2.

Energetics for the First Step of the Decomposition of Urea Assisted by One Water Molecule Leading to the H₃NCONH Zwitterion (Int2)

	PDDG	PDDG GB/SA	QM/MM MC/FEP	B3LYP/6-311++G**	MP2/6-311++G** ICPMd
ΔE‡ (ZPE-corrected), kcal/mol	53.3b			27.3	24.6
ΔE‡0= ΔE‡ + ΔEthermala				23.2
ΔH‡ = ΔE‡ + ΔnRT, kcal/mol				23.2
ΔG‡ = ΔH‡ − TΔ S, kcal/mol				26.6	24.9
ΔG‡solution = ΔG‡ + ΔΔGsolvation		34.2b,c	21.1	26.4c	23.1

^aE_thermal = E_vibtational + E_rotational + E_{translational}.

^bVibrational frequencies were not calculated at the PDDG level.

^cThe values include the ΔG of hydration obtained from the GB/SA model.

^dResults from Ref. 17.