  Detached WD+MS PCEBs are perhaps the most suitable objects for testing
predictions of close-compact binary-star evolution theories, in particular, CE
evolution. The population of WD+MS PCEBs has been simulated by several authors
in the past and compared with observations. However, most of those predictions
did not take the possible contributions to the envelope ejection from
additional sources of energy (mostly recombination energy) into account. Here
we update existing binary population models of WD+MS PCEBs by assuming that a
fraction of the recombination energy available within the envelope contributes
to ejecting the envelope. We performed Monte Carlo simulations of 10^7 MS+MS
binaries for 9 different models using standard assumptions for the initial
primary mass function, binary separations, and initial-mass-ratio distribution
and evolved these systems using the publicly available BSE code. Including a
fraction of recombination energy leads to a clear prediction of a large number
of long orbital period (>~10 days) systems mostly containing high-mass WDs. The
fraction of systems with He-core WD primaries increases with the CE efficiency
and the existence of very low-mass He WDs is only predicted for high values of
the CE efficiency (>~0.5). All models predict on average longer orbital periods
for PCEBs containing C/O-core WDs than for PCEBs containing He WDs. This effect
increases with increasing values of both efficiencies. Longer periods after the
CE phase are also predicted for systems containing more massive secondary
stars. The initial-mass-ratio distribution affects the distribution of orbital
periods, especially the distribution of secondary star masses. Our simulations,
in combination with a large and homogeneous observational sample, can provide
constraints on the values of the CE efficiencies, as well as on the
initial-mass-ratio distribution for MS+MS binary stars.
