  While most scintillation-based dark matter experiments search for Weakly
Interacting Massive Particles (WIMPs), a sub-GeV WIMP-like particle may also be
detectable in these experiments. While dark matter of this type and scale would
not leave appreciable nuclear recoil signals, it may instead induce ionization
of atomic electrons. Accurate modelling of the atomic wavefunctions is key to
investigating this possibility, with incorrect treatment leading to a large
suppression in the atomic excitation factors. We have calculated these atomic
factors for argon, krypton and xenon and present the tabulated results for use
with a range of dark matter models. This is made possible by the separability
of the atomic and dark matter form factor, allowing the atomic factors to be
calculated for general couplings; we include tables for vector, scalar,
pseudovector, and pseudoscalar electron couplings. Additionally, we calculate
electron impact total ionization cross sections for xenon using the tabulated
results as a test of accuracy. Lastly, we provide an example calculation of the
event rate for dark matter scattering on electrons in XENON1T and show that
these calculations depend heavily on how the low-energy response of the
detector is modelled.
