Calculation of hydrogen physisorption affinity to graphene species with ab-intio and density-functional methods

The physisorption strength of molecular hydrogen to graphene structures is investigated with the density-functional theory (DFT), the Moller-Plesset second-order perturbation and the coupled-cluster singles and doubles with perturbative triples correction (CCSD(T)). While the DFT with the generalized gradient approximation largely fails to describe the binding energetics, the local density approximation (LDA) qualitatively captures the overall binding features of the van der Waals interactions. Our calculations of H-2 binding to large graphene species show that the DFT with the LDA somewhat consistently overestimates the binding energy by about 30 % and underestimates the binding distance by about 9 % compared to more accurate and more highly correlated methods like the CCSD(T). However, for small graphene systems, the DFT and more highly correlated methods exhibit a substantial discrepancy, which can be attributed to the non-negligible self-interaction errors in the DFT.