  In this work we apply entropic sampling simulations to a three-state model
which has exact solutions in the microcanonical and grand-canonical ensembles.
We consider $N$ chains placed on an unidimensional lattice, such that each site
may assume one of three-states: empty (state 1), with a single molecule
energetically null (state 2), and with a single molecule with energy
$\varepsilon$ (state 3). Each molecule, which we will treat here as dimers,
consists of two monomers connected one to each other by a rod. The
thermodynamic properties, such as internal energy, densities of dimers and
specific heat were obtained as functions of temperature where the analytic
results in the micro-canonical and grand-canonical ensembles were successfully
confirmed by the entropic sampling simulations.
