  Extending our previous work, we explore the breathing mode---the [uniform]
radial expansion and contraction of a spatially confined system. We study the
breathing mode across the transition from the ideal quantum to the classical
regime and confirm that it is not independent of the pair interaction strength
(coupling parameter). We present the results of time-dependent Hartree-Fock
simulations for 2 to 20 fermions with Coulomb interaction and show how the
quantum breathing mode depends on the particle number. We validate the accuracy
of our results, comparing them to exact Configuration Interaction results for
up to 8 particles.
