  Energy loss in collisions of charged projectiles with many-electron systems
can be dealt with in time-dependent density functional theory by invoking
Ehrenfest's theorem for the time evolution of expectation values of
observables. We derive an exact expression for the evaluation of energy loss
for systems described in a target reference frame, which is a functional of the
electron density. Using an approximation scheme we then apply the expression to
antiproton-atom collisions at intermediate and high energies within the
framework of the basis generator method. The calculations are performed within
the semiclassical approximation for the nuclear motion, and a straight-line
trajectory is employed. The energy loss is evaluated from an expectation value
of the time derivative of the time-dependent projectile potential and avoids
the problem of identifying the excited and ionized many-electron contributions
in the many-electron wavefunction. There is also no need to invoke the
independent-event model, since the calculations are performed within the
framework of the independent-electron mean-field model. Detailed comparisons
are provided for net ionization and total energy loss of antiprotons colliding
with hydrogen, helium, neon, carbon, nitrogen and oxygen. Reasonable agreement
is found with the results from one-electron and two-electron calculations for
atomic hydrogen and helium, and with experiment in the latter case. For the
$\bar p - \rm Ne$ system at intermediate collision energies we find
discrepancies with previous work that included only single-electron
transitions. The sequence of results for C, N, O, Ne allows one to paint a
consistent picture which awaits experimental verification.
