An exact expression for the exchange kernel (the frequency-dependent functional derivative of the exchange potential with respect to the electron density) is derived. For the correlation kernel a coupling-constant expansion is presented. A modified coupled Kohn-Sham equation for an efficient “exact-exchange” calculation of dynamic polarizabilities and excitation energies is suggested.

• Received 16 July 1997

DOI:https://doi.org/10.1103/PhysRevA.57.3433