Today we learned in the ABC of DFT about Hartree Fock.
Finding the wave function for all electrons is difficult because the electrons push on each through a Coulomb force. It would be advantageous to calculate the wave function of one electron with the others stationary and then calculate the rest of the electrons sequentially. Once you go around the set of electrons a few times, then things will stop changing and you have a good approximation as to where the electrons should be. One way to do this is by writing the wave function as a Slater determinant.
Density Functional Theory is all about approximations, and there are a lot of them, so I'll try to keep you in the loop, diary.