  We have investigated the far-infrared dipole modes of a quantum antidot
submitted to a perpendicularly applied magnetic field B. The ground state of
the antidot is described within local spin-density functional theory, and the
spectrum within time-dependent local spin-density functional theory. The
results are compared with those corresponding to a quantum dot of similar
electronic surface density. The method is able to reproduce two of the more
salient experimental features, namely that main bulk and edge modes have the
same circular polarization, and that the negative B dispersion edge branch
oscillates, having minima at the B values corresponding to fully occupied
Landau levels. It fails, however, to yield the unique feature of short-period
antidot lattices that the energy of the edge magnetoplasmon approaches the
cyclotron frequency for small B. The existence of anticyclotron polarized bulk
modes is discussed, and a detailed account of the dipole spin mode is
presented.
