Table 3.

The total energy (a.u.) of the mixed dimer (2-HPY–2-PY) and the transition state (T.S.) and the activation energies (kJ/mol) for the double proton transfer of the 2-HPY and 2-PY tautomers using different DFT) functionals with 6-311++G** and aug-cc-pvdz basis sets.

Functional	Basis Set	2-HPY–2-PY	T.S.	Activ. Energy
B3LYP	6-311++G**	−647.2530	−647.2398	33.532
	aug-cc-pvdz	−647.1573	−647.1452	30.372
CAM-B3LYP	6-311++G**	−646.9344	−646.9214	32.632
	aug-cc-pvdz	−646.8367	−646.8249	29.62
ωB97XD	6-311++G**	−647.0232	−647.0091	35.392
	aug-cc-pvdz	−646.9371	−646.9239	33.532
M062X	6-311++G**	−646.9798	−646.9688	27.612
	aug-cc-pvdz	−646.9088	−646.8989	24.848