Correlation energy functional and potential from time-dependent exact-exchange theory.

In this work we studied a new functional for the correlation energy obtained from the exact-exchange (EXX) approximation within time-dependent density functional theory. Correlation energies have been calculated for a number of different atoms showing excellent agreement with results from more sophisticated methods. These results lose little accuracy by approximating the EXX kernel by its static value, a procedure which enormously simplifies the calculations. The correlation potential, obtained by taking the functional derivative with respect to the density, turns out to be remarkably accurate for all atoms studied. This potential has been used to calculate ionization potentials, static polarizabilities, and van der Waals coefficients with results in close agreement with experiment.