Essential Density Functional Theory

Abstract Starting with an explanation of what functionals and functional derivatives are, this chapter develops the basic functional calculus needed to understand density functional theory (DFT). DFT for electrons in condensed matter is then explained, starting with the Thomas–Fermi model in which the kinetic energy is a local functional of the density. The Hohenberg–Kohn–Sham DFT is then developed, leading to the Schr ö dinger–like Kohn–Sham equations. The local density approximation (LDA) for exchange and correlation is explained. The chapter includes an introduction to the self-consistent solution of the Kohn–Sham equations.