Physisorption of H₂ on Fullerenes and the Solvation of C₆₀ by Hydrogen Clusters at Finite Temperature: A Theoretical Assessment

Abstract

The interaction between hydrogen and carbonaceous nanostructures is of fundamental interest in various areas of physical chemistry. In this contribution we have revisited the physisorption of hydrogen molecules and H clusters on fullerenes, following a first-principles approach in which the interaction is quantitatively evaluated for the C system using high-level electronic structure methods. Relative to coupled cluster data at the level of single, double, and perturbative triple excitations taken as a benchmark, the results for rotationally averaged physisorbed H show a good performance of MP2 variants and symmetry-adapted perturbation theory, but significant deviations and basis set convergence issues are found for dispersion-corrected density functional theory. These electronic structure data are fitted to produce effective coarse-grained potentials for use in larger systems such as C-H. Using path-integral molecular dynamics, the potentials are also applied to parahydrogen clusters solvated around fullerenes, across the regime where the first solvation shell becomes complete and as a function of increasing temperature. For C our findings indicate a sensible dependence of the critical solvation size on the underlying potential. As the temperature is increased, a competition is found between the surface and radial expansions of the solvation shell, with one molecule popping away at intermediate temperatures but getting reinserted at even higher temperatures.

Solvation of coronene oligomers by para-H2 molecules: the effects of size and shape

“…The present article was concerned with the uptake of parahydrogen on larger cationic assemblies of coronene molecules, aiming to determine from computational modeling the sizes at which the first solvation shell closes and the influence of both the size of the assembly and its specific shape on this limiting size. Our atomistic approach relies on a polarizable force field for the para-H 2 molecules whose interaction with the hydrocarbon atoms was calibrated on quantum chemical results, 35,37 combined with a chemically realistic model for the cationic assembly based on fluctuating charges. 25 Combining a classical survey of the low-energy structures by global optimization followed by path-integral molecular dynamics simulations to account for the main nuclear quantum effects, we have calculated the binding energy and the main structural features of cationic oligomers coated by increasing numbers of para-hydrogen molecules, also taking into account several isomers that the hydrocarbon assembly possibly exhibits.…”

“…As in our former investigations [35][36][37] we used a united-atom model for para-hydrogen for both structural and path-integral molecular dynamics computations. This is justified by the experimental situation we are referring to, in which the coronene cations coated by hydrogen are initially generated into the cryogenic medium of helium nanodroplets.…”

“…In this study we notably aim at characterizing the size of the solvation shell of hydrogen molecules coating cationic coronene oligomers. Following our earlier investigations of hydrogen uptake on individual PAH molecules, [35][36][37] we first employ geometric criteria to achieve this characterization, by examining the distribution of the (minimum) distance between the para-H 2 molecules to the various atoms of the solute. The minimum distance is a more appropriate quantity than the distance to the center of the solute owing to the strongly aspherical character of polyaromatic molecules.…”

“…In earlier work, we computationally examined the solvation of various carbonaceous molecules by para-hydrogen and orthodeuterium, including coronene and other PAHs ranging from benzene to circumcoronene, 35 as well as fullerenes. 36,37 The carbonaceous dopants were modeled at the atomistic level but treated as rigid, the hydrogen molecules being described as pointlike and interacting with each other through the long established Silvera-Goldman (SG) potential. 38 The interaction between the dopant and the hydrogen molecules was modeled from a pairwise additive contribution from repulsion and dispersion terms, plus a vectorial polarization term acting on the solvent molecules arising from the multipolar distribution on the dopant set as partial atomic charges.…”

“…This potential was fitted to reproduce quantum chemistry (QC) results, and in a separate contribution the issue of the most appropriate QC method for such systems was discussed separately. 37 After identifying candidate structures using classical global optimization, quantum nuclear effects were subsequently included with pathintegral molecular dynamics (PIMD) simulations.…”