Monte Carlo study of multicomponent monolayer adsorption on square lattices

The monolayer adsorption process of interacting binary mixtures of species $A$ and $B$ on square lattices is studied through grand canonical Monte Carlo simulation in the framework of the lattice-gas model. Four different energies have been considered in the adsorption process: 1) $\epsilon_0$, interaction energy between a particle (type $A$ or $B$) and a lattice site; 2) $w_{AA}$, interaction energy between two nearest-neighbor $A$ particles; 3) $w_{BB}$, interaction energy between two nearest-neighbor $B$ particles; 4) $w_{AB}=w_{BA}$, interaction energy between two nearest-neighbors being one of type $A$ and the other of type $B$. The adsorption process has been monitored through total and partial isotherms and differential heats of adsorption corresponding to both species of the mixture. Our main interest is in the repulsive lateral interactions, where a variety of structural orderings arise in the adlayer, depending on the interaction parameters ($w_{AA}$, $w_{BB}$ and $w_{AB}$). At the end of this work, we determine the phase diagram characterizing the phase transitions occurring in the system. A nontrivial interdependence between the partial surface coverage of both species is observed.