  We investigate a semiclassical momentum density energy functional for atoms
and show that it yields the same value as the well-known Thomas-Fermi
functional. In fact, we show an explicit relation between the minimizers of the
two functionals. The main result is that the atomic momentum density converges
on the scale $Z^{2/3}$ to the minimizer of the momentum density energy
functional. This allows to determine the linear response of atoms on momentum
dependent perturbations.
