Charge transfer between atoms and surfaces in time-dependent processes: what about the different treatments of the electronic correlation effects?

EVELINA A. GARCÍA; E. C. GOLDBERG

San Carlos de Bariloche, Río Negro, Argentina, November 6-10

Conferencia; 13th International Conference on Solid Films and Surfaces (ICSFS-13); 2006

It has been found in a very simple model system for describing the charge transfer between atoms and surfaces in a time-dependent process, that different perturbative treatments of the intra-atomic Coulomb repulsion (U) are able to reproduce the exact values of the atom charge states [1-2]. A perturbative calculation up to a second order in the correlation parameter (U) is used for those situations in which this one can be considered small compared with the atom-surface hopping term (V) [1]. While, an infinite-U limit approximation is used in the opposite case [2]. A realistic atom-surface interacting system involves shifts and widths of the atom energy levels that change with the distance; and also surfaces with finite bandwidths and energy dependent density of states. Therefore, different relations between the intra-atomic correlation and the atom-surface hopping are present along the whole time evolution. An interesting and largely studied collisional system is Hydrogen against an Al surface [3]. A single-electron picture based on the spin-less approximation represents a first attempt to calculate the ion fractions in this case. But this kind of approximation does not take into account the spin fluctuation statistics in the neutralization of either proton or negative ions. The infinite-U limit appears as the appropriate one for contemplating this effect. By the other hand, if the close encounter region is defining the charge transfer, the perturbative treatment up to a second order in the diminished value of U near to the surface, seems more adequate. This work is justly devoted to the calculation of  the charge state probabilities in Hydrogen scattering from an Al surface by considering these different treatments of the intra-atomic correlation. A detailed and comparative analysis is performed in order to understand and isolate the effects coming from the distance dependence of energy level shifts and widths, the energy dependence of the surface density of states, the electron-electron interaction and the quantum time evolution.  [1] E. C. Goldberg and M. C. G. Passeggi, J. Phys.: Condens. Matter  8, 7637 (1996). [2] E. C. Goldberg, F. Flores, and R. C. Monreal, Phys. Rev. B71, 035112 (2005). [3] M. Maazouz, R. Baragiola, A. Borisov, V. A. Esaulov, S. Lacombe, J. P. Gauyacq, L. Guillemot, and D. Teillet-Billy, Surf. Sci. 364, L568 (1996).