Universal Dynamical Steps in the Exact Time-Dependent   Exchange-Correlation Potential
  We show that the exact exchange-correlation potential of time-dependent density-functional theory displays dynamical step structures that have a spatially non-local and time non-local dependence on the density. Using one-dimensional two-electron model systems, we illustrate these steps for a range of non-equilibrium dynamical situations relevant for modeling of photo-chemical/physical processes: field-free evolution of a non-stationary state, resonant local excitation, resonant complete charge-transfer, and evolution under an arbitrary field. Lack of these steps in usual approximations yield inaccurate dynamics, for example predicting faster dynamics and incomplete charge transfer. 
Peter Elliott, Johanna I. Fuks, Angel Rubio, Neepa T. Maitra
physics.chem-ph cond-mat.mtrl-sci cond-mat.other