Benchmark calculations with correlated molecular wave functions. VII. Binding energy and structure of the HF dimer

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Abstract
The hydrogen bond energy and geometry of the HF dimer have been investigated using the series of correlation consistent basis sets from aug‐cc‐pVDZ to aug‐cc‐pVQZ and several theoretical methods including Mo/ller–Plesset perturbation and coupled cluster theories. Estimates of the complete basis set (CBS) limit have been derived for the binding energy of (HF)2 at each level of theory by utilizing the regular convergence characteristics of the correlation consistent basis sets. CBS limit hydrogen bond energies of 3.72, 4.53, 4.55, and 4.60 kcal/mol are estimated at the SCF, MP2, MP4, and CCSD(T) levels of theory, respectively. CBS limits for the intermolecular F–F distance are estimated to be 2.82, 2.74, 2.73, and 2.73 Å, respectively, for the same correlation methods. The effects of basis set superposition error (BSSE) on both the binding energies and structures have also been investigated for each basis set using the standard function counterpoise (CP) method. While BSSE has a negligible effect on the intramolecular geometries, the CP‐corrected F–F distance and binding energy differ significantly from the uncorrected values for the aug‐cc‐pVDZ basis set; these differences decrease regularly with increasing basis set size, yielding the same limits in the CBS limit. Best estimates for the equilibrium properties of the HF dimer from CCSD(T) calculations are De=4.60 kcal/mol, RFF=2.73 Å, r1=0.922 Å, r2=0.920 Å, Θ1=7°, and Θ2=111°.