Derivation of an electron-proton correlation functional for multicomponent density functional theory within the nuclear-electronic orbital approach

Multicomponent density functional theory enables the quantum mechanical treatment of electrons and selected hydrogen nuclei. An electron-proton correlation functional is derived from the electron-proton pair density associated with a recently proposed ansatz for the explicitly correlated nuclear-electronic wave function. This ansatz allows the retention of all terms in the pair density, and the resulting functional is expected to scale properly and to be computationally efficient. Applications to model systems illustrate that it provides accurate nuclear densities.