Exact density functional obtained via the Levy constrained search

Abstract

A stochastic minimization method for a real-space wavefunction, $Ψ({\bf r}_{1},{\bf r}_{2}\ldots{\bf r}_{n})$, constrained to a chosen density, $ρ({\bf r})$, is developed. It enables the explicit calculation of the Levy constrained search $F[ρ]=\min_{Ψ\rightarrowρ}\langleΨ|\hat{T}+\hat{V}_{ee}|Ψ\rangle$ (Proc. Natl. Acad. Sci. 76 6062 (1979)), that gives the exact functional of density functional theory. This general method is illustrated in the evaluation of $F[ρ]$ for two-electron densities in one dimension with a soft-Coulomb interaction. Additionally, procedures are given to determine the first and second functional derivatives, $\frac{δF}{δρ({\bf r})}$ and $\frac{δ^{2}F}{δρ({\bf r})δρ({\bf r}')}$. For a chosen external potential, $v({\bf r})$, the functional and its derivatives are used in minimizations only over densities to give the exact energy, $E_{v}$ without needing to solve the Schrödinger equation.