  DFT calculations have become widespread in both chemistry and materials,
because they usually provide useful accuracy at much lower computational cost
than wavefunction-based methods. All practical DFT calculations require an
approximation to the unknown exchange-correlation energy, which is then used
self-consistently in the Kohn-Sham scheme to produce an approximate energy from
an approximate density. Density-corrected DFT is simply the study of the
relative contributions to the total energy error. In the vast majority of DFT
calculations, the error due to the approximate density is negligible. But with
certain classes of functionals applied to certain classes of problems, the
density error is sufficiently large as to contribute to the energy noticeably,
and its removal leads to much better results. These problems include reaction
barriers, torsional barriers involving $\pi$-conjugation, halogen bonds,
radicals and anions, most stretched bonds, etc. In all such cases, use of a
more accurate density significantly improves performance, and often the simple
expedient of using the Hartree-Fock density is enough. This article explains
what DC-DFT is, where it is likely to improve results, and how DC-DFT can
produce more accurate functionals. We also outline challenges and prospects for
the field.

Chemical Physics