Assessing the reliability of van der Waals DFT functionals to study the physisorption of molecular hydrogen on aromatic systems

Abstract

The physisorption of $\hbox {H}_2$ on organic molecules has received much attention during the 2000s, because they are the elementary bricks of the organic linkers in isoreticular metal–organic frameworks, materials that are considered as very promising ones for hydrogen storage. Here, we have studied the physisorption of $\hbox {H}_2$ on a wide variety of aromatic molecules, from pure and substituted benzene to polycyclic hydrocarbons, by means of density functional theory (DFT). In performing DFT calculations, we have taken of the relatively new family of functionals that include van der Waals (vdW) effects. We have performed our calculations with two different approaches: (1) the one proposed by Grimme et al. (J Chem Phys 132:154104, 2011), DFT+D3, which corrects the total energy; (2) the one proposed by Lundqvist et al. (Phys Rev B 82:081101, 2010), vdW+DF2, which corrects the correlation energy. From the comparison between our DFT vdW energies and the ones obtained by means of ab initio theory methods [MP2 and CCSD(T)], we conclude that DFT in combination with the vdW+DF2 functional yields reliable binding energies of $\hbox {H}_2$ to aromatic complexes, at a much smaller computational cost. Hopefully, our results will stimulate further studies on these kinds of systems, which have been hampered due to limited computational resources.