MP2[V] - A Simple Approximation to Second-Order Møller-Plesset Perturbation Theory.

We propose a simplified variant of the dual-basis MP2[K] scheme [ J. Chem. Phys. 2011, 134, 081103] that bootstraps a small-basis MP2 result to a large-basis one. This simplified method, which we call MP2[V], assumes the occupied orbitals are adequately described by the smaller basis, and, therefore, only the relaxation of the virtual orbitals is considered when shifting to the larger basis. Numerical tests on several organic reactions and noncovalent interactions show that MP2[V] yields absolute and relative energies that are in excellent agreement with the conventional large-basis MP2 calculations but in a small fraction of the time.