  Post-asymptotic giant branch (post-AGB) stars with discs are all binaries.
Many of these binaries have orbital periods between 100 and 1000 days so cannot
have avoided mass transfer between the AGB star and its companion, likely
through a common-envelope type interaction. We report on preliminary results of
our project to model circumbinary discs around post-AGB stars using our binary
population synthesis code binary_c. We combine a simple analytic thin-disc
model with binary stellar evolution to estimate the impact of the disc on the
binary, and vice versa, fast enough that we can model stellar populations and
hence explore the rather uncertain parameter space involved with disc
formation. We find that, provided the discs form with sufficient mass and
angular momentum, and have an inner edge that is relatively close to the
binary, they can both prolong the life of their parent post-AGB star and pump
the eccentricity of orbits of their inner binaries.
