Chemical bonding without orbitals

This work presents an implementation of the original orbital-free Hohenberg-Kohn density functional theory in a form that is able to predict chemical bonding in molecules. The method is completely parameter-free and does not require analytical functional approximations. Instead, the proposed method is based on the idea that atoms are meaningful pieces of a molecule and thus, a promolecule, build from frozen spherical atomic entities, serves as a suitable model for the latter. This idea is imposed on the physical equations, originating from density functional theory converted into a bifunctional formalism. The viewpoint proposed in this study offers a new strategic way of subsequent approximation levels in orbital free density functional theory. In this work the zeroth order approximation is shown to predict chemical bonding in molecules, providing a concept of the chemical bond without involving orbitals.