# Density Functional Theory

Density Functional Theory DFT is a reformulation of Hartree-Fock in terms of a joint electron density

• $\rho (x)=\int\psi^2(x,x_2,...,x_N)dx_2...dx_N$,

which introduces a new contribution (from Slater determinants) to the total energy named exchange-correlation energy $EC(\rho )$. The dependence of $EC(\rho )$ on $\rho$ is unknown and DFT thus relies on predictions of EC based on Hartree-Fock and thus DFT has the same limitations as Hartree-Fock, albeit at (somewhat) smaller computational cost.