Ab initio theory of spin entanglement in atoms and molecules

We investigate spin entanglement in many-electron systems within the framework of density functional theory. We show that the entanglement length, which is extracted from the spatial dependence of the local concurrence, is a sensitive indicator of atomic shells and reveals the character, covalent or metallic, of chemical bonds. These findings shed light on the remarkable success of modern density functionals, which tacitly employ the entanglement length as a variable. This opens the way to further research on entanglement-based functionals.