In the latter case, ρ el is a distribution that is assumed to be supported in Ω and is represented in terms of basis functions arising from the interfaced QM-code. In practical calculations, however, ρ el is not supported in Ω due to the Gaussian-or Slater-type basis functions having tails that extend beyond the molecular cavity and any electronic charge on the complement of Ω is lost, a problem known as the escaped charge problem . This problem has been extensively studied and has been found not to be an issue in practical applications.