Signatures of multiple jumps in surface diffusion on honeycomb surfaces

The jump distribution, a property of the motion of adsorbates on a corrugated surface, contains crucial information on adsorbate-substrate energy dissipation processes. To provide a means to study jump distributions in a honeycomb array of adsorption sites, we derive analytical expressions for the intermediate scattering function (ISF) describing jump diffusion taking into account jumps up to fourth-nearest neighbor in length. To enable testing the analytical expressions against experimental or simulated data, we develop a global fitting routine that can be applied to experimental or simulated ISFs to infer multiple jumps. We demonstrate the analysis method by studying the jump distribution arising from classical Langevin molecular dynamics simulations of two model systems, cyclopentadienyl (Cp) on Cu(111), and deuterium (D) on Pd(111). The simulations and analysis confirm that diffusion of Cp/Cu(111) at a surface temperature T-s = 135 K takes place in a regime of predominantly single jumps. Classical simulations of D/Pd(111) at T-s = 350 K, with a realistic Langevin friction, suggest that the diffusion of D/Pd(111) involves a high proportion of multiple jumps. The parameters that apply to D/Pd(111) are typical of the interaction of hydrogen atoms with close-packed transition metal surfaces, suggesting that long jumps are a general feature of the high temperature surface diffusion of hydrogen.