  When applied to a single nucleon, nuclear energy density functionals may
yield a non-vanishing internal energy thus implying that the nucleon is
interacting with itself. It is shown how to avoid this unphysical feature for
semi-local phenomenological functionals containing all possible bilinear
combinations of local densities and currents up to second order in the
derivatives. The method outlined in this Rapid Communication could be easily
extended to functionals containing higher order terms, and could serve as a
guide for constraining the time-odd part of the functional.
