3. to avoid the problem that the exchange potential is not directly accessible in terms of the Kohn-Sham orbitals. With the OEP method, functional derivatives of orbital-dependent energy expressions, including -for example, the Kohn-Sham exchange potential -are accessible. While basis-set OEP methods were numerically problematic in the past, robust, numerically stable basis-set OEP methods are now available. Moreover, orbital-dependent functionals can be evaluated in a post-self-consistent-field (post-SCF) manner, avoiding the need to take functional derivatives of orbital-dependent functionals with respect to the electron density. Alternatively, functional derivatives can be taken with respect to orbitals instead of the electron density, leading to generalized Kohn-Sham methods.