Simulation Data from: The EOS/Resolution Conspiracy: Convergence in Proto-Planetary Collision Simulations

We investigate how the choice of equation of state (EOS) and resolution
conspire to affect the outcomes of giant impact (GI) simulations. We focus
on the simple case of equal mass collisions of two Earth-like 0.5ME
proto-planets showing that the choice of EOS has a profound impact on the
outcome of such collisions as well as on the numerical convergence with
resolution. In simulations where the Tillotson EOS is used, impacts
generate an excess amount of vapour due to the lack of a thermodynamically
consistent treatment of phase transitions and mixtures. In oblique
collisions this enhances the artificial angular momentum (AM) transport
from the planet to the circum-planetary disc reducing the planet’s
rotation period over time. Even at a resolution of  1.3x106
particles the result is not converged. In head-on collisions the lack of a
proper treatment of the solid/liquid-vapour phase transition allows the
bound material to expand to very low densities which in turn results in
very slow numerical convergence of the critical specific impact energy for
catastrophic disruption QRD with increasing resolution as reported in
prior work. The simulations where ANEOS is used for oblique impacts are
already converged at a modest resolution of 105 particles, while head-on
collisions converge when they evidence the post-shock formation of a dense
iron-rich ring, which promotes gravitational re-accumulation of material.
Once sufficient resolution is reached to resolve the liquid-vapour phase
transition of iron in the ANEOS case, and this ring is resolved, the value
of QRD has then converged.