  Modeling the couplings between active particles often neglects the possible
many-body effects that control the propulsion mechanism. Accounting for such
effects requires the explicit modeling of the molecular details at the origin
of activity. Here, we take advantage of a recent two-dimensional model of
isotropic active particles whose propulsion originates from the interactions
between solute particles in the bath. The colloid catalyzes a chemical reaction
in its vicinity, which results in a local phase separation of solute particles,
and the density fluctuations of solute particles cause the enhanced diffusion
of the colloid. In this paper, we investigate an assembly of such active
particles, using (i) an explicit model, where the microscopic dynamics of the
solute particles is accounted for; and (ii) an implicit model, whose parameters
are inferred from the explicit model at infinite dilution. In the explicit
solute model, the effective diffusion coefficient of the active colloids
strongly decreases with density, an effect which is not captured by the derived
implicit model. This suggests that classical models, which usually decouple
pair interactions from activity, fail to describe collective dynamics in active
colloidal systems driven by solute-solute interactions.
