Accurate Quantum Chemical Description of Non-Covalent Interactions in Hydrogen Filled Endohedral Fullerene Complexes

Abstract

The structures and binding energies of encapsulated dihydrogen in C60 and C70 have been studied by accurate quantum chemical models with large basis sets and/or extrapolation techniques. Methods based on modified perturbation theory (up to third order) as well as state-of-the-art double-hybrid density functionals have been applied. The proper inclusion of London dispersion interactions is mandatory in order to obtain accurate and consistent energies. It is found that for C60 only one H2 molecule exothermically (binding energy of −7 kcal/mol with an estimated uncertainty of ±1 kcal/mol) fits into the cage, while two H2 molecules become just unbound within the theoretical error bars. Results for the C70 cage show that complexation of two H2 can take place with a relatively large binding energy of −11 kcal/mol. Simple dispersion corrected density functionals (e.g., PBE-D) yield in general very good results (deviations <10−20% of ΔE) compared to our best reference values.