  The two-dimensional Active Brownian Particles system is meant to be composed
of hard disks, that show excluded volume interactions, usually simulated via
molecular dynamics using pure repulsive potentials. We show that the softness
of the chosen potential plays a role in the result of the simulation, focusing
on the case of the emergence of Motility Induced Phase Separation. In a pure
hard-sphere system with no traslational diffusion,the phase diagram should be
completely determined by their density and P\'eclet number. However, we have
found two additional effects that affect the phase diagram in the ABP model we
simulate: the relative strength of the traslational diffusion compared to the
propulsion term and the overlapping of the particles. As we show, the second
effect can be strongly mitigated if we use, instead of the standard
Weeks-Chandler- Andersen potential, a harder one, the pseudo-hard spheres
potential. Moreover, in determining the boundary of our phase space, we have
tried different approaches to detect MIPS and concluded that observing
dynamical features, via the non-Gaussian parameter, is more efficient than
observing structural ones, via the local density distribution function. We also
demonstrate that the Vogel-Fulcher equation successfully reproduces the decay
of the diffusion as a function of density, except for very high density cases.
Thus, the ABP system behaves similarly to a fragile glass in this regard.
