Accurate interaction energies by spin component scaled Möller-Plesset second order perturbation theory calculations with optimized basis sets (SCS-MP2mod): Development and application to aromatic heterocycles

The Spin Component Scaled (SCS) MP2 method using a reduced and optimized basis set (SCS-MP2mod) is employed to compute the interaction energies of nine homodimers, formed by aromatic heterocyclic molecules (pyrrole, furan, thiophene, oxazole, isoxazole, pyridine, pyridazine, pyrimidine, and pyrazine). The coefficients of the same-spin and opposite-spin correlation energies and the Gaussian type orbitals (GTO) polarization exponents of the 6-31G basis set are simultaneously optimized in order to minimize the energy differences with respect to the coupled-cluster with single, double and perturbative triples excitations [CCSD(T)] reference interaction energies, extrapolated to a complete basis set. It is demonstrated that the optimization of the spin scale factors leads to a noticeable improvement of the accuracy with a root mean square deviation less than 0.1 kcal/mol and a largest unsigned deviation smaller than 0.25 kcal/mol. The pyrrole dimer provides an exception, with a slightly higher deviation from the reference data. Given the high benefit in terms of computational time with respect to the CCSD(T) technique and the small loss of accuracy, the SCS-MP2mod method appears to be particularly suitable for extensive sampling of intermolecular potential energy surfaces at a quantum mechanical level. Within this framework, a transferability test of the SCS-MP2mod parameters to a benchmark set of this class of molecules is very promising as the reference interaction energies of several heterocyclic aromatic heterodimers were reproduced with a standard deviation of 0.30 kcal/mol. The SCS-MP2mod remarkably outperforms the value of 1.95 kcal/mol obtained with standard MP2/6-31G.