Interaction between atoms and surfaces: A bond-pair description based on an extended Anderson model

Abstract

A bond-pair model Hamiltonian developed previously for systems consisting of interacting atoms is applied to describe atom-surface interactions. By proposing a mixed basis set involving localized adatom orbitals ͕ ␣ ͖ and extended surface states ͕ k ͖, and by application of a mean-field approximation, the Hamiltonian is reduced to the form of the single-particle Anderson model. The resulting model Hamiltonian is free from adjustable parameters. These parameters include both the effects of electronic interactions between the atom and the solid and those arising from the lack of orthogonality between the adsorbate and substrate orbitals. The nonlocal exchange contributions are treated consistently within the Hartree-Fock method, while valencelike and corelike band states are also taken into account. This model is applied to consider the interaction of hydrogen with metals ͑Al, Li, and Na͒. The results for chemisorption are in good agreement with those obtained by other theoretical approaches based on either the density functional theory or embedding cluster methods, as well as with existing experimental data. In addition, the calculation of the shifts and widths of the adsorbate levels in an ample range of separation distances are also in good agreement with those obtained by using atomic physics techniques. ͓S0163-1829͑98͒10031-0͔

Image Potential State Influence on Charge Exchange in Li+–Metal Surface Collisions

“…The total energies are calculated without allowing charge exchange between the atom and surface, the Li energy level variation being caused by overlap and mean-field electrostatic interactions. The effect of the long-range interactions is introduced by considering the image potential defining the behavior for large normal distances (z) to the surface (z > z a ) 57 The wave vectors k ⃗ = (k ⃗ // ,k z ), which classify the bulk and surface-like states ψ k ⃗ (r⃗ ) of a solid with surface, are only Bloch vectors in the parallel direction to the surface (k ⃗ // ). The coupling term V k ⃗ ,2s in the case of bulk and intrinsic surface 59 states is calculated as usual according to the expansion of ψ k ⃗ (r⃗ ) in atomic orbitals centered on the surface atoms (ϕ i (r⃗ − R ⃗ s )) The coefficients c i,R ⃗ s k ⃗ determine the density matrix elements …”

Ion fractions in the scattering of hydrogen on different reconstructed silicon surfaces

“…The model proposed for the atom-surface interaction can be thought as a generalization of the interaction between two atoms, where one of them consist of a system having a large basis set {u k } (including extended valence and core-like states) [44]. The description is based on the symmetric orthogonalization procedure [47], in which starting from a non-orthogonal basis set {u k , u a } (u k and u a correspond to states of the isolated subsystems), the application of ð1 þ SÞ À 1 2 , where S is the overlap matrix produces the desired orthonormal basis set {U k , U a }.…”

“…Thus, by using a lineal combination of atomic orbitals (LCAO) for the substrate states and performing a mean-field approximation on the many-body interaction terms, one arrives to the orbital energies E r a and hopping term T r ak (see Ref. [44] for a more detailed description):…”

“…The calculation is based on a detailed description of the interaction parameters for the system H-Si, and also by using a realistic density of states for the reconstructed surfaces obtained with the code FIRE-BALL96 [43]. The energy and hopping terms are obtained from a bond-pair approximation to the Hamiltonian that describes the projectile-surface interacting system [44]. As the natural reference frame is provided by the surface, the relative orientations of the projectile orbital states with reference to the surface plane cannot be ignored if one looks for a correct description of the angular dependence of the charge transfer process.…”

Scattering of F atoms and anions on a TiO2(110) surface

“…In the case of metals charge transfer is generally described in a delocalised, jellium model type, free electron description of the solid . Resonant electron transfer processes are quite well understood in this framework and recently more sophisticated treatments have been presented [24,[27][28][29]. In the case of ionic solids on the other hand the strongly localised nature of alternating positive and negative charges prompted a different molecular type description involving a non-resonant electron transfer [45,47] process.…”