  Aiming to approach the thermodynamical properties of hard-core systems by
standard molecular dynamics simulation, we propose setting a repulsive
constant-force for overlapping particles. That is, the discontinuity of the
pair potential is replaced by a linear function with a large negative slope.
Hence, the core-core repulsion, usually modeled with a power function of
distance, yields a large force as soon as the cores slightly overlap. This
leads to a quasi-hardcore behavior. The idea is tested for a triangle potential
of short range. The results obtained by replica exchange molecular dynamics for
several repulsive forces are contrasted with the ones obtained for the
discontinuous potential and by means of replica exchange Monte Carlo. We found
remarkable agreements for the vapor-liquid coexistence densities as well as for
the surface tension.
