Several Theorems in Time-Dependent Density Functional Theory

The time dependence of the exchange-correlation energy in density functional theory is given in terms of the exchange-correlation potential. The virial theorem for the exchange-correlation potential is shown to hold for time-dependent electronic systems and is illustrated by an exactly solved model: Hooke's atom with a time-dependent force constant. A relation between the coupling constant and functionals evaluated on scaled densities is derived.