  We apply hydrodynamic evaporation models to different synthetic planet
populations that were obtained from a planet formation code based on a
core-accretion paradigm. We investigated the evolution of the planet
populations using several evaporation models, which are distinguished by the
driving force of the escape flow (X-ray or EUV), the heating efficiency in
energy-limited evaporation regimes, or both. Although the mass distribution of
the planet populations is barely affected by evaporation, the radius
distribution clearly shows a break at approximately 2 $R_{\oplus}$. We find
that evaporation can lead to a bimodal distribution of planetary sizes (Owen &
Wu 2013) and to an "evaporation valley" running diagonally downwards in the
orbital distance - planetary radius plane, separating bare cores from low-mass
planet that have kept some primordial H/He. Furthermore, this bimodal
distribution is related to the initial characteristics of the planetary
populations because low-mass planetary cores can only accrete small primordial
H/He envelopes and their envelope masses are proportional to their core masses.
We also find that the population-wide effect of evaporation is not sensitive to
the heating efficiency of energy-limited description. However, in two extreme
cases, namely without evaporation or with a 100\% heating efficiency in an
evaporation model, the final size distributions show significant differences;
these two scenarios can be ruled out from the size distribution of $Kepler$
candidates.
