Atom-surface scattering calculations

The summation of pair-wise potentials is a good approximation for molecular dynamics calculations for simple classical many-body problems [27], It has been widely used to simulate hyperthennal energy (>1 eV) atom-surface scattering ... 

A thermal energy atomic beam (20-200 meV) has a wavelength on the order of inter-atomic distances. The atomic beam diffracts from a contour of the surface potential corresponding to the beam energy. This contour is located 3-4 A above the ion cores in the outermost layer of the surface. Atomic beam diffraction patterns are normally interpreted using model surface scattering calculations, where the scattering is described as a Van der Waals interaction. 

Inelasticity in atom surface scattering can be included in a phenomenological way by including an imaginary part in the atom surface potential. In a recent calculation we used a potential of... 

In this article approximate theoretical results are used to correlate certain features of the atom-surface scattering intensity with important properties of the atom-surface potential. These qualitative considerations allow information about the atom surface potential to be extracted directly from the data with a minimum of theoretical calculation. This information may be used to develop a very precise form for the atom-surface interaction. In the cases where these calculations have been performed the resulting potential appears to be in excellent agreement with other experimental information. 

Based on the data of hydrogen and oxygen atoms scattering by the surface of ZnO film obtained by the method of atom beams we calculated the degree of ionization of chemosorbed particles on the film using the variation of its conductivity (see Table 3.1) [23]. 

Figure 5 shows DOS from self-consistent field, full multiple scattering calculations as implemented in the FEFF8 code33 on the supported Ptio cluster illustrated. The support is mimicked by the 3 water molecules as shown the O atoms represent the O atoms in the support, and the H atoms effectively terminate the cluster and represent the Si or A1 atoms such as that in a zeolite. The DOS are shown from calculations with and without a core-hole on the 3 different site symmetries (surface, edge, and center). 

The development of theory for reliable calculations of chemical dynamics has two components the construction of accurate, ab initio, multidimensional potential energy surfaces (PESs) and the performance of reactive scattering calculations, either by time-independent (TI) or time-dependent (TD) methods, on these surfaces. Accurate TI quantum methods for describing atom-diatom reactions, in particular for the benchmark H + H2 reaction, have been achieved since 1975.[1,2,3] Many exact and approximate theories have been tested with the H + H2 reaction.[4,5]... 

For all but the very smallest systems, (such as HeH and even there it is very expensive), it is not possible in practice to calculate the full potential surface, with a grid fine enough that it can be directly used for solving the (nuclear) dynamical problem in Van der Waals molecules (or for scattering calculations). Moreover, such a numerical potential would not be convenient for most purposes. Therefore, one usually represents the potential by some analytical form, for instance, a truncated spherical expansion (1) or another type of model potential (cf. sect. 2). The parameters in this model potential can be obtained by fitting the ab initio results for a limited set of intermolecular distances and molecular orientations. Since we have encountered some difficulties in this fitting procedure which we expect to be typical, we shall describe our experience with the ( 2114)2 and (N2)2 cases in some detail. At the same time, we use the opportunity to make a few comments about the convergence of the spherical expansion used for (Njjj and about the validity of the atom-atom model potential applied to both ( 2114)2 and (Njjx. 

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