Ab initio study of the effects of orientation and corrugation for H2 adsorbed on polycyclic aromatic hydrocarbons

Abstract

This paper reports state-of-the-art ab initio calculations at the second order of Moller-Plesset perturbation theory of molecular hydrogen interaction with polycyclic aromatic hydrocarbons (PAHs) up to coronene (C(24)H(12)). The effects of both H(2) orientation with respect to the PAH plane and of PAH corrugation have been carefully investigated. It was found that the energetic preference for the perpendicular H(2) orientation over the parallel one decreases rapidly as the PAH grows. The detailed study of coronene-H(2) potential energy surface has made it possible to estimate from first principles the graphite-H(2) binding energy. This ab initio estimate is shown to be in fair agreement with experiment. As revealed by the example of benzene-H(2) dimer, the electrostatic energy component plays an important role in PAH-H(2) interactions, that stems largely from the charge penetration effect and, therefore, cannot be reproduced by the simple quadrupole-quadrupole interaction model.

DFT/CCSD(T) Investigation of the Interaction of Molecular Hydrogen with Carbon Nanostructures

“…This value differs substantially from the MP2 bond length of 0.767 , and compares well with the experimental value of 0.7414 . Thus, the difference between the reported MP2/CBS binding energy of 5.13 kJ mol À1 for the most stable configuration (B1z) and the corresponding value of Donchev [4] (5.32 kJ mol…”

“…Recently, large discrepancies between the previously published MP2/AVQZ results for the benzene···H 2 complex have been reported. [4] The detailed analysis revealed that these discrepancies stem mainly from the choice of the HÀH internuclear separation. Herein, we have aimed at the CCSD(T)/CBS description of hydrogen interactions with various graphitic surfaces and therefore have used a CCSD(T)/ AVQZ internuclear separation of 0.742 .…”

“…The periodic DFT calculations were performed with the Vienna ab initio simulation package (VASP). [52] A slightly modified notation of Donchev [4] has been adopted for geometry definition. One-dimensional scans of the PES were performed as indicated in Figure 2 with a hydrogen center of mass over the (1)-center of the ring, (2)-center of the bond, and (3)-atom.…”

“…The value of 5.5 kJ mol À1 is a laterally averaged estimate taken from the coronene model and as such is not directly related to the other theoretical predictions. Considering a general trend towards lower energy differences between the various adsorption sites on large PAH and graphite PESs, the averaging procedure of Donchev [4] based on the coronene model seems to overestimate the effect of hydrogen dynamics on graphitic surfaces slightly. Nevertheless, it is clear that an experimental binding energy of 5.00 AE 0.05 kJ mol À1 should be considered as the lower limit of the exact theoretical value.…”

“…The second-order Møller-Plesset (MP2) approach [19] is frequently used for benchmark calculations of weakly bound complexes, even though the MP2 method typically overestimates the interaction energies and underestimates the equilibrium distances for these systems. [4,6,7] Modeling the interaction of the adsorbed molecules with carbon nanomaterials requires very large polycyclic aromatic hydrocarbon (PAH) models to obtain converged results. The MP2 or spin-component scaled MP2 (SCS-MP2) methods [20] with appropriate basis sets can only be applied to medium-sized PAHs (typically coronene-like models), even when exploiting the resolution of identity (RI) approximation.…”