Kieron Burke, Neepa Maitra, and Ivo Souza
Dept of Chemistry and Chemical Biology and
Dept of Physics and Astronomy, Rutgers University

In 1995, Gonze, Ghosez, and Godby, showed that the periodic density in a bulk insulator in an external electric field does not uniquley determine the external potential, leading to an ultra-nonlocal dependence of the macroscopic exchange-correlation electric field on the density. By considering the situation from a time-dependent viewpoint, we explain the origin of this effect and show why the current-density is the appropriate variable for describing this phenomenon. No ultra-nonlocality is needed in a time-dependent current density functional theory.