Runge-Gross action-integral functional re-examined

Abstract

The density-based action-integral functional introduced by Runge and Gross [Phys. Rev. Lett. 52, 997(1984)] in their foundation of time-dependent density-functional theory (TDDFT) is re-examined. Based on an obvious expansion of the original definition, it becomes apparent that the action-integral functional is both trivial and non-stationary. It cannot be used to establish equations of motion for the time-evolution of quantum systems at the density-function level.