Spin-Component Scaling Methods for Weak and Stacking Interactions.

New scaling parameters are presented for use in the spin-component scaled (SCS) variant of density fitted local second-order Møller-Plesset perturbation theory (DF-LMP2) that have been optimized for use in evaluating the interaction energy between nucleic acid base pairs. The optimal set of parameters completely neglects the contribution from antiparallel-spin electron pairs to the MP2 energy while scaling the parallel contribution by 1.76. These spin-component scaled for nucleobases (SCSN) parameters are obtained by minimizing, with respect to SCS parameters, the rms interaction energy error relative to the best available literature values, over a set of ten stacked nucleic acid base pairs. The applicability of this scaling to a wide variety of noncovalent interactions is verified through evaluation of a larger set of model complexes, including those dominated by dispersion and electrostatics.