Density-Polarization-Functional Theory and Long-Range Correlation in Dielectrics

The novel density-polarization-functional theory proposed by Gonze et al. [Phys. Rev. Lett. 74, 4035 (1995)] addresses the electronic ground state of a macroscopic dielectric, with or without an applied external field. In a crystalline system the exchange-correlation energy per cell may have a dependence on macroscopic polarization, in addition to the one on the periodic density. I prove that whenever this happens, the many-body electronic wave function displays long-range correlation.