A perturbation theory study of H2 on LiF(0 0 1)

In response to recent helium atom scattering (HAS) results, Monte Carlo (MC) simulations and perturbation theory have been performed for H2 on LiF(0 0 1). MC simulations predict that H2 molecules form a series of structures, p(2 × 2), p(8 × 2), p(4 × 2) with coverages Θ = 0.5, 0.625 and 0.75, respectively, that are stable up to 8 K. This is in partial agreement with the HAS results that report c(2 × 2) and c(8 × 2) structures; they agree in terms of coverage and stability, but disagree in terms of symmetry. To reconcile the results of the simulations and experiments, the orientation of the adsorbed H2 molecules was studied using perturbation theory. These calculations show that the adsorbed H2 molecules are azimuthally delocalized and that the structures are c-type rather then p-type. The calculations also indicate that p-H2 and helicoptering o-H2 prefer cationic sites, while cartwheeling o-H2 prefers anionic sites.