Simulation of delocalized exchange by local density functionals

Exchange holes in molecules can be delocalized over several centers, thus throwing into question their approximation by local density functionals. This work introduces a simple model which detects delocalization in molecules through a local variable related to kinetic energy density. A local exchange functional is derived that reproduces exact-exchange atomization energies of molecules with relatively low error. This has important implications for the simplification of "hybrid" density-functional theories which contain an exactly computed exchange term. (C) 2000 American Institute of Physics. [S0021-9606(00)30209-4].