THEORY OF ADSORPTION AND DESORPTION IN HIGH ELECTRIC-FIELDS

A new method is proposed which allows the inclusion of strong electric fields into Car-Parrinello-like total-energy calculations. As a first application we calculated for the adsorption of Na on Al(111) the cha nges in atomic geometry, binding energies and diffusion barriers due t o the influence of electrostatic fields. For high fields below the eva poration field strength a strong outward relaxation of the adsorbate i s found which clearly reduces the energy differences between different adsorption sites and the diffusion barriers. This results in a degene racy of the on-top and fcc hollow positions whereas in the field free case the fcc site is preferred by 0.1 eV.