  Due to efficient scaling with electron number N, density functional theory
(DFT) is widely used for studies of large molecules and solids. Restriction of
an exact mean-field theory to local potential functions has recently been
questioned. This review summarizes motivation for extending current DFT to
include nonlocal one-electron potentials, and proposes methodology for
implementation of the theory. The theoretical model, orbital functional theory
(OFT), is shown to be exact in principle for the general N-electron problem. In
practice it must depend on a parametrized correlation energy functional.
Functionals are proposed suitable for short-range Coulomb-cusp correlation and
for long-range polarization response correlation. A linearized variational
cellular method (LVCM) is proposed as a common formalism for molecules and
solids. Implementation of nonlocal potentials is reduced to independent
calculations for each inequivalent atomic cell.
