# Exact kinetic energy functional for general many-electron systems

## TL;DR

This paper derives the exact kinetic energy functional for general many-electron systems using a two-density model, addressing a longstanding challenge in orbital-free density functional theory.

## Contribution

It introduces a novel two-density model approach that yields the exact kinetic energy functional, improving the theoretical foundation of orbital-free DFT.

## Key findings

- Exact kinetic energy functional derived for many-electron systems.
- Functional includes previously suggested functionals, excluding Thomas-Fermi.
- Advances orbital-free DFT by providing a precise functional form.

## Abstract

The exact form of the kinetic energy functional has remained elusive in orbital-free models of density functional theory (DFT). This has been the main stumbling block for the development of a general-purpose framework on this basis. Here, we show that on the basis of a two-density model, which represents many-electron systems by mass density and spin density components, we can derive the exact form of such a functional. The exact functional is shown to contain previously suggested functionals to some extent, with the notable exception of the Thomas-Fermi kinetic energy functional.