  Multicomponent density functional theory (DFT) enables the consistent quantum
mechanical treatment of both electrons and protons. A major challenge has been
the design of electron-proton correlation functionals that produce even
qualitatively accurate proton densities. Herein an electron-proton correlation
functional, epc17, is derived analogously to the Colle-Salvetti formalism for
electron correlation and is implemented within the nuclear-electronic orbital
(NEO) framework. The NEO-DFT/epc17 method produces accurate proton densities
efficiently and is promising for diverse applications.
