But this is just one strategy. It is possible to determine additionally other contributions to the energy from the orbitals -for example, parts of the exchange energy in hybrid methods -or even to calculate all contributions to the energy exactly from the occupied orbitals, except the correlation energy. The latter can then be approximated by orbital-dependent functionals. In the latter case, the density is not needed at all in the calculation of the total DFT energy. If, furthermore, the orbitals are obtained via the optimized-effective-potential (OEP) method or within an appropriate generalized Kohn-Sham approach, then DFT methods results that do not require at any point the calculation of the density. The density is then only required in the underlying formalism.