Image potential states on lithium, copper and silver surfaces

The electronic structure of the Li(110) surface is calculated within the self-consistent pseudopotential method. The calculation does not give any occupied surface state. At the same time, unoccupied resonance surface states have been found at the <(Gamma) over bar> point and along the <(PH) over bar> symmetry direction. Image potential slates with energies of E-1 = -0.73 eV and E-2 = -0.22 eV are predicted al the Gamma point. For the description of the image potential stales, we propose a one-dimensional model potential. The parameters of this potential are determined with the use of experimental (or first-principles calculation) values of the width and position of the energy gap at the <(Gamma)over bar> point and the energies E-0 and E-1 of the surface state and first image potential state, respectively. Using this model potential, we study the binding energies, wave functions and lifetime of image potential states on the Li(110), Cu(100), Cu(lll), Ag(100) and Ag(111) surfaces. We also show that using the local part of the full, screened, non-local pseudopotential can produce incorrect results for the binding energy of the image slates. (C) 1997 Elsevier Science B.V.