  Protoplanets develop via collisions between planetesimals and planetary
embryos in the final assembly stage of planet formation. The efficiency of the
planet formation can be defined by the mass ratio between formed protoplanets
and the initial mass of embryos and planetesimals. In final assembly planet
formation models, the gravitational interactions between planetesimals are
usually neglected due to computational difficulties, namely, computations
require fewer resources in this way. We investigated the effect of this
simplification via modeling the planet formation efficiency in a circumstellar
belt of embryos and self-interacting or non-self-interacting planetesimals. We
used our own developed GPU-based direct N-body integrator, HIPERION, for the
simulations. We found that planet formation efficiency is higher if the
planetesimal self-interaction is taken into account in models that contain the
commonly used 100 embryos. The observed effect can be explained by the damping
of planetesimal eccentricities by their self-gravity. The non-self-interacting
and self-interacting models show qualitatively the same results if the initial
number of embryos is above 200.
