Studies in Time-Dependent Correlation Functions.

Alexander L. Fetter

Paul Hessler, Jang Park, Kieron Burke

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.

Shu Tanaka, Seiji Miyashita

We study how the degree of ordering depends on the strength of the thermal and quantum fluctuations in frustrated systems by investigating the correlation function of the order parameter. Concretely, we compare the equilibrium spin correlation function in a frustrated lattice which exhibits a nonmonotonic temperature dependence (reentrant type dependence) with that in the ground state as a function of the transverse field that causes the quantum fluctuation. We find the correlation function in the ground state also shows a nonmonotonic dependence on the strength of the transverse field. We also study the real-time dynamics of the spin-correlation function under a time-dependent field. After sudden decrease in the temperature, we found nonmonotonic changes of the correlation function reflecting the static temperature dependence, which indicates that an effective temperature of the system changes gradually. For the quantum system, we study the dependence of changes of the correlation function on the sweeping speed of the transverse field. Contrary to the classical case, the correlation function varies little in a rapid change of the field, though it shows a nonmonotonic change when we sweep the field slowly.

Jurgen Michael Honig, Józef Spałek

Peter Millington

James W. Dufty

The long-time behavior of space- and time-dependent correlation functions is obtained including the ring contributions or correlated two-body effects. The latter give rise to anomalous hydrodynamic effects and persistent correlations in the nonhydrodynamic part.