High level Ab inito bench mark computaions on weak interactions (H2)2 dimer revisited

Abstract

The Potential Energy Surface PES of (H₂)₂ dimer has been investigated, using five simple rigid rotor models. These models are called: head to head, symmetric side to side, L , steplike and T model. All calculations were done at two levels of ab initio methods: MP2(Full) and QCISD (T,Full) using cc-pVTZ basis set at singlet state of spin multiplicity. The results of scanning PES were then fitted to Taylor series up to 15 terms to obtain the equilibrium distances and interaction energies between pairs of H₂ molecules.The standard deviation of the residuals in fitting procedure is well below 10^-⁹ in all cases.L model has been found to be the most stable one instead of previously reported T model and 7 times more stable than other models.The validity of hard sphere approximation was also tested by solving simple mathematical equation and found to be no longer valid in these interactions.