Table 3.

Computed binding energies and energy components (kcal/mol) between H₅O₂⁺ and (H₂O)₄ using the iterative charge-updating optimization and variational multilevel X-Pol methods. The 6-31G(d) basis set is used in all calculations at the M06/MG3S optimized geometries.

H5O2+	(H2O)4	ΔEdist	ΔEint	ΔEele	ΔEXD	ΔEb
	X-Pol optimization by iteratively updating MK charges
M06	M06	11.4	−100.5	−89.1	18.4	−70.7
M06	B3LYP	11.4	−99.0	−87.7	18.4	−69.3
M06	HF	11.3	−103.3	−92.0	18.4	−73.6
MP2	HF	10.9	−103.8	−92.9	18.4	−74.5
CCSD	M06	11.1	−100.6	−89.5	18.4	−71.1
	X-Pol optimization by iteratively updating MPA charges
M06	M06	11.5	−99.0	−87.5	18.4	−69.1
M06	B3LYP	11.4	−96.6	−85.2	18.4	−66.8
M06	HF	11.4	−103.1	−91.7	18.4	−73.3
MP2	HF	11.1	−103.7	−92.7	18.4	−74.3
CCSD	M06	11.2	−99.2	−88.0	18.4	−69.6
	X-Pol by variational optimization with MPA charges
M06	M06	10.7	−101.7	−91.0	18.4	−72.6
M06	B3LYP	11.3	−99.4	−88.1	18.4	−69.7
M06	HF	11.3	−105.8	−94.5	18.4	−76.1
MP2	HF	12.3	−106.7	−94.4	18.4	−76.0
CCSD	M06	18.5	−102.4	−83.9	18.4	−65.5
	Full wave function calculation without fragmentation
CCSD(T)a						−69.7

^aComputed at CCSD(T)/MG3S//M062X/MG3S.