Searching for DFT-based methods that include dispersion interactions to calculate the physisorption of H2 on benzene and graphene.

Abstract

Simulations of the hydrogen storage capacities of nanoporous carbons require an accurate treatment of the interaction of the hydrogen molecule with the graphite-like surfaces of the carbon pores, which is dominated by the dispersion forces. These interactions are described accurately by high level quantum chemistry methods, like the Coupled Cluster method with single and double excitations and a non-iterative correction for triple excitations (CCSD(T)), but those methods are computationally very expensive for large systems and for massive simulations. Density functional theory (DFT)-based methods that include dispersion interactions at different levels of complexity are less accurate, but computationally less expensive. In order to find DFT-methods that include dispersion interactions to calculate the physisorption of H2 on benzene and graphene, with a reasonable compromise between accuracy and computational cost, CCSD(T), Møller-Plesset second-order perturbation theory method, and several DFT-methods have been used to calculate the interaction energy curves of H2 on benzene and graphene. DFT calculations are compared with CCSD(T) calculations, in the case of H2 on benzene, and with experimental data, in the case of H2 on graphene. Among the DFT methods studied, the B97D, RVV10, and PBE+DCACP methods yield interaction energy curves of H2-benzene in remarkable agreement with the interaction energy curve obtained with the CCSD(T) method. With regards to graphene, the rev-vdW-DF2, PBE-XDM, PBE-D2, and RVV10 methods yield adsorption energies of the lowest level of H2 on graphene, very close to the experimental data.