Ground state electronic density, effective Kohn-Sham potential, and sketch of the photoemission process. (a) Upper panel, ground state electronic density in units of the positive background density (dashed line, r
= 4) for a cluster containing 20 electrons; lower panel, the corresponding effective Kohn-Sham potential and occupied energy levels. (b) Sketch of the photoemission process. An electron and a hole are created at the center of the spherical cluster at t = 0. Both are represented by classical point particle and the electron starts to move along the z-axis with velocity υ0.