Anisotropic nonadditive ab initio force field for noncovalent interactions of H2.

A quantum mechanical polarizable force field (QMPFF) has been applied to the noncovalent interactions of molecular hydrogen as well as closed-shell monoatomic species (CSMS): rare gases, alkali cations, and halide anions. The importance of all the main energy components is demonstrated: electrostatics (including penetration effect), exchange repulsion, dispersion, and induction. As the MP2 level of quantum mechanics, which is used to parametrize QMPFF, significantly underestimates the H2-H2 dimer binding energy, the force field was refined using state-of-the-art CCSD(T) data. The approach demonstrates excellent transferability, which is confirmed by accurate reproduction of mixed H2-CSMS dimers and the second virial coefficient of hydrogen vapor.