On the accuracy of spin-component-scaled perturbation theory (SCS-MP2) for the potential energy surface of the ethylene dimer

The bimolecular interaction potentials for various configurations of the ethylene dimer computed with coupled-cluster and spin-component-scaled second-order Moller-Plesset perturbation theory (SCS-MP2) are reported. With a triple-zeta basis set including diffuse functions, SCS-MP2 improves over the results of conventional MP2. However, when the resulting energies are counterpoise-corrected for overbinding due to basis-set superposition error or obtained with a quadruple-zeta basis set, the MP2 results are superior. Alternative scaling parameters for SCS-MP2 have been determined from computations performed across the potential energy surface. These scaling parameters are found to be relatively insensitive to the relative configuration of the monomers and to include a slightly larger relative weighting of the same-spin electron pairs than originally proposed by Grimme [J. Chem. Phys. 118, 9095 ( 2003)]. The opposite-spin and same-spin parameters that minimize errors in the SCS-MP2 results for the ethylene dimer are C(OS) = 1.28 and C(SS) = 0.50, respectively. With these alternative scaling parameters, the CCSD(T) potential energy curves for ethylene dimer are well reproduced for all configurations.