Spatial cusps in initial wavefunctions can lead to non-analytic behavior in
time. We suggest a method for calculating the short-time behavior in such
situations. For these cases, the density does not match its Taylor-expansion in
time, but the Runge-Gross proof of time-dependent density functional theory
still holds, as it requires only the potential to be time-analytic.Comment: 5 pages, 1 figur