Both of the latter are functions of the electron density, P The simplest models are called local spin density or local density models, and ll be referred to as SVWN(Slater, Vosko, Wilk, Nusair) models. Here, the form of the exchange and correlation functionals follows from the exact(numerical) solution of a many-electron gas of uniform density, as a function of the density, by subtracting core and Coulomb from the total energy(there is no Enuclear term).