  A number of direct detection experiments are searching for electron
excitations created by scattering of sub-GeV dark matter. We present an
alternate formulation of dark matter-electron scattering in terms of the
dielectric response of a material. For dark matter which couples to electrons,
this approach automatically accounts for in-medium screening effects, which
were not included in previous rate calculations for semiconductor targets. We
show that the screening effects appear for both scalar and vector mediators.
The result is a non-negligible reduction of reach for direct detection
experiments which use dielectric materials as targets. We also explore
different determinations of the dielectric response, including first-principles
density functional theory (DFT) calculations and a data-driven analytic
approximation using a Mermin oscillator model.
