The performance of MP2.5 and MP2.X methods for nonequilibrium geometries of molecular complexes

Here we test the performance of the newly developed MP2.5 and MP2.X methods in terms of their abilities to generate accurate binding energies for noncovalently bound complexes at points away from their minimum energy structures and in terms of the accuracy of their potential energy minima. The MP2.X method is a scaled version of MP2.5 that allows for the use of smaller basis sets for the most computationally demanding (MP3) term, significantly reducing its computational cost. MP2.5 and MP2.X binding energy errors are compared to those of the reference CCSD(T)/CBS method on the dissociation curves associated with the S66 dataset of noncovalent complexes (S66x8). It is found that both the MP2.5 and MP2.X methods produce binding energy errors, as well as potential energy minima, that are significantly more accurate than those of MP2 methods. Thus, these methods are appropriate choices when very high quality geometries of noncovalent complexes are required.