Position Dependent Dielectric Function Near the Cu Surface

In the study of the local electric field enhancement near the metal surface, it would be important to investigate the behavior of the dielectric function in the vacuum region near the metal surface. We calculate the position dependent dielectric function near the Cu(100) surface and demonstrate that there is a long-lived tail of the dielectric function out of the surface, which provides clear evidence of the field enhancement. The calculated dielectric function depends on the directions of the oscillating electric field and the system.