Table 2.

Computed binding energies and energy components (kcal/mol) between acetic acid (A) and water (B) using the variational 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	ΔEele	ΔEXDa	ΔEb
		X-Pol by variational optimization with MPA charges
M06	M06	2.8	−10.1	−13.5	−11.8	−9.0	2.0	−7.0
M06	B3LYP	2.6	−9.7	−13.0	−11.3	−8.7	2.0	−6.7
M06	HF	3.1	−10.7	−14.2	−12.5	−9.4	2.0	−7.4
MP2	HF	4.3	−11.5	−13.1	−12.3	−8.0	2.0	−6.0
CCSD	M06	3.8	−11.0	−12.6	−11.8	−8.0	2.0	−6.0
		Full wave function calculation without fragmentation
M06a								−6.9
CCSD(T)b								−6.6

^aThe exchange-dispersion energy is estimated using the Buckingham terms with the parameters A_OO =1.5221×10⁵ kcal/mol, B_OO = 3.754 Å⁻¹, and C_OO = 756.3 Å⁶ kcal/mol for oxygen, and A_CC = 2.50178 ×10⁶ kcal/mol, B_CC = 4.384 Å⁻¹, and C_CC = 1533.1 Å⁶ kcal/mol for carbon.

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