Table 1.

Computed binding energies and energy components (kcal/mol) between acetic acid (A) and water (B) using iterative charge-updating optimization in multilevel X-Pol. The 6-31G(d) basis set is used in all calculations at the M06/MG3S optimized geometries.

A	B	ΔEdist	$\mathrm{\Delta }{E}_A^{\text{int}}(B)$	$\mathrm{\Delta }{E}_B^{\text{int}}(A)$	ΔEint	ΔEba
	X-Pol optimization by iteratively updating MK charges
M06	M06	1.4	−9.1	−7.8	−8.4	−7.0
M06	B3LYP	1.4	−8.9	−7.6	−8.2	−6.8
M06	HF	1.6	−9.4	−8.2	−8.8	−7.2
MP2	HF	1.2	−8.8	−7.8	−8.3	−7.1
CCSD	M06	1.0	−8.7	−7.7	−8.2	−7.2
	X-Pol optimization by iteratively updating MPA charges
M06	M06	1.5	−9.6	−8.7	−9.2	−7.7
M06	B3LYP	1.5	−9.2	−8.5	−8.8	−7.3
M06	HF	1.8	−10.2	−9.2	−9.7	−7.9
MP2	HF	1.3	−9.5	−8.4	−9.0	−7.7
CCSD	M06	1.1	−9.1	−8.3	−8.7	−7.6
	Full wave function calculation without fragmentation
M06b						−6.9
CCSD(T)b						−6.6

^aFor the purposes of this table, the multilevel X-Pol calculations of ΔE_b are set equal to ΔE_ele, that is, they include the change in intramonomer energy and the electrostatic interaction energy but not the intermonomer exchange repulsion and dispersion terms

^bComputed using the MG3S basis set at the M062X/MG3S geometries.