5. Overview of the calculation framework

5.1 Density functional theory

The Density Functional Theory (DFT) developed in 1964 and 1965 by Hohenberg, Kohn and Sham won Kohn the Nobel Prize in Chemistry in 1998, crowning the theory's success in solving problems at different scales in chemistry and physics. It is a quantum theory that reduces the many-electron problem (multibody) to a one-electron problem in an effective field.

DFT states that the total energy E of a system of electrons, interacting under the influence of an external potential, is given exactly and uniquely by a ground-state electron density functional: E = E [ρ]. What does the term functional mean? Since ρ is in fact ρ (r ), i.e. a function of spatial coordinates, then E is the function of a function. In the DFT theorems, it was shown...