A physical interpretation of the Kohn-Sham energy in time-dependent current-density functional theory

It is well known that in static density functional theory the Kohn-Sham energy plays a fundamental role because it gives, by construction, the ground state energy of the system under study. In time-dependent density functional theory, it is not possible to attach to the Kohn-Sham energy the same physical interpretation. For example we know that for an isolated system the Kohn-Sham energy can be ``dissipated'' while the total energy of the real system is conserved.$^{1}$ However, the Kohn-Sham energy can be given a new physical interpretation as the maximum work that can be extracted from the system and it is related to the production of entropy during the time evolution of the system.$^{1}$ Project supported by NFS Grant No. DMR-0313681\\ $^{1}$R. D'Agosta and G. Vignale, accepted by Phys. Rev. Lett., cond-mat/0508175