Exchange and correlation in finite-temperature TDDFT

We discuss the finite-temperature generalization of time-dependent density functional theory (TDDFT). The theory is directly analogous to that at temperature T = 0. For example, the finite-T TDDFT exchange-correlation kernel fxc(T, n) in the local density approximation can again be expressed as a density derivative of the exchange correlation potential fxc(T, n) = [∂vxc(T, n)∕∂n]δ(r − r′), where n = N∕V is the electron number density. An approximation for the kernel fxc(T, n) is obtained from the finite-T generalization of the retarded cumulant expansion applied to the homogeneous electron gas. Results for fxc and the loss function are presented for a wide range of temperatures and densities including the warm dense matter regime, where T ≈ TF, the electron degeneracy temperature. The theory also permits a physical interpretation of the exchange and correlation contributions to the theory