Role of van der Waals forces in the diffraction of noble gases from metal surfaces

Abstract

The role of van der Waals (vdW) forces in the description of scattering processes of noble gases from metal surfaces is currently under debate. Although features of the potential energy surface such as anticorrugation or adsorption energies are sometimes found to be well described by standard density functional theory (DFT), the performance of DFT to describe diffraction spectra may rely on the accuracy of the vdW functionals used. To analyze the precise role of these vdW forces in noble gas diffraction by metal surfaces, we have thoroughly studied the case of Ne/Ru(0001), for which accurate experimental results are available. We have carried out classical and quantum dynamics calculations by using DFT-based potentials that account for the effect of vdW interactions at different levels of accuracy. From the comparison of our results with experimental data, we conclude that the inclusion of vdW effects is crucial to properly describe diffraction of noble gases from metal surfaces. We show that among the vdW-DFT functionals available in the literature, not all of them can be used to accurately describe this process. DOI: 10.1103/PhysRevB.93.060301The diffraction of noble gases is largely used in surface science as a nondestructive analytical tool to investigate, for example, surface morphology and surface phonons (see Refs. [1,2] and refs. therein). Furthermore, this tool can also be used to study the dynamics of adsorbate/surface systems [3,4]. In order to extract the maximum amount of information from experimental diffraction spectra, a detailed comparison with theoretical simulations is often desirable. However, from a theoretical point of view, the description of the electronic structure of noble-gas atom/surface systems, in particular when metal surfaces are involved, is not a trivial matter due to the possible prominent role of van der Waals (vdW) interactions. The first theoretical approach to treat these kind of systems was reported in the early 80's by Esbejerg and Nørskov [5], who proposed the use of an interaction potential proportional to the unperturbed electron density of the substrate at the position of the atomic projectile. But this approach was questioned only two years later by experimental results showing anticorrugation effects in He scattering from Ni(110) [6] that could not be reproduced with this simple model. Later on, in the 90's, first principles calculations were performed using a jellium model to describe the substrate [7,8]. Although this simple model is good enough to reproduce some general properties, to take into account the lattice structure is essential to analyze many other properties such as the corrugation amplitudes of the system, which are responsible for diffraction scattering phenomena.The periodic lattice structure of a noble-gas atom/surface system can be well described by density functional theory (DFT) with periodic boundary conditions. However, standard DFT functionals do not include, per se, the effect of the van * fernando.martin@uam.es † cristina.diaz@uam.es der W...

Elastic and inelastic diffraction of fast atoms, Debye-Waller factor, and Mössbauer-Lamb-Dicke regime

“…The VdW attraction also has been neglected and is certainly important in the 10-50 meV [14,52,54,64] in the form of the Beeby correction [44] where the effective impact energy is E ⊥ = E sin 2 θ + E V dW with E V dW the depth of the potential energy well. The VdW attraction also influences the shape of the binary potential V (r) and may affect the local value of Γ(E ⊥ ) as illustrated in [25,64].…”

Atom-surface van der Waals potentials of topological insulators and semimetals from scattering measurements

“…It is generally recognised that vdW corrected functionals consistently improve the adsorption energies of molecules and noble gases both on insulating and metallic surfaces 55, 56 and can lead to a good agreement with scattering experiments 57 . On the other hand, a recent comparison between experimentally measured and theoretically predicted diffraction probabilities, shows how these functionals can give rise to large overestimations of the corrugation, i.e.…”

“…Considering also the challenges theorists are facing in describing the vdW interaction correctly, CC calculations in combination with the three-dimensional CMP are clearly a sensitive tool for determining the atom-surface interaction potential, at least in the case of conducting surfaces. Although some functionals have been proven to yield good results for diffraction from alkali metal surfaces 63,64 , Ne diffraction 57 and physisorption energies in He/metal systems 58 , the performance for HAS from conducting surfaces is still under debate 65 . As noted by del Cueto et al 65 , up to now none of the available vdW functionals have been proven to yield good He diffraction probabilities, most probably due to the in 1.2 described overestimation of the long-distance corrugation which is probed by the He atom 65 .…”

Experimental and theoretical study of rotationally inelastic diffraction of H2(D2) from methyl-terminated Si(111)

“…Diffraction probabilities are computed herein by solving the time-dependent Schrödinger (TDS) equation of the nuclear Hamiltonian using the multi-configuration time-dependent Hartree (MCTDH) method 63,64 which has already been successfully used to study diffraction of atomic projectiles, 65 as well as reactive scattering of molecular projectiles. [66][67][68] In the MCTDH method, the nuclear wavefunction is written as a sum of products of single-particle functions (SPFs).…”