Interaction energies of dispersion-bound methane dimer from coupled cluster method at complete basis set limit

We have calculated the interaction energy function of the dispersion-bound methane dimer at the minimum-energy D-3d conformation using the coupled cluster with single and double and perturbative triple excitations [CCSD(T)] method at complete basis set (CBS) limit. With Dunning's correlation-consistent polarized valence basis sets (cc-pVXZ and aug-cc-pVXZ, X = D, T, Q), we estimated the CCSD(T)/CBS potential curve using several analytical extrapolation methods on the potential data over the entire potential curve. The relative performance of these extrapolation methods has been carefully evaluated. With varying quality of the basis sets used, more consistent estimations of the CCSD/CBS potential curve are obtained using the methods of Helgaker et al. and Martin than using the method of Feller. (c) 2008 Elsevier B.V. All rights reserved.