The main barrier to automating multiconfigurational approaches is automatically selecting the active space in a robust fashion. Methods for automatically selecting active spaces continue to be an active research topic, and several approaches exist. Here, we employ approximate pair coefficient (APC) selection, in which candidate Hartree-Fock orbitals are ranked for the active space by means of their approximate pair coefficient interaction with other orbitals. Given doubly occupied orbitals i and virtual orbitals a, approximate pair coefficients are calculated as