What is Density Functional Theory?
Density Functional Theory (DFT) was developed in the 1960s by Walter Kohn, amongst various others. The chief discovery was that the total energy of a system of electrons in an external potential is a unique functional of the groundstate density; if you find the density, then you can calculate the energy. Unfortunately this functional is not known, but it turns out that even relatively crude approximations can give excellent results. The particular “external potential” we are interested in is that generated by nuclei, but this is not necessary for density functional theory itself.
