  We devise an efficient practical method for computing the Kohn-Sham
exchange-correlation potential corresponding to a Hartree-Fock electron
density. This potential is almost indistinguishable from the exact-exchange
optimized effective potential (OEP) and, when used as an approximation to the
OEP, is vastly better than all existing models. Using our method one can obtain
unambiguous, nearly exact OEPs for any finite one-electron basis set at the
same low cost as the Krieger-Li-Iafrate and Becke-Johnson potentials. For all
practical purposes, this solves the long-standing problem of black-box
construction of OEPs in exact-exchange calculations.
