Simulações entrópicas para um modelo tipo ZGB dependente da temperatura

Abstract

The ZGB model is a simple model built to describe some known steps of the CO−O2 reaction on a catalytic surface, which is represented in the model by a square lattice of side L. The main events that occur are the adsorption of monoxide molecules CO and O2 oxygen at empty sites of the lattice, which occur, respectively, with probabilities y and 1−y . Another important event is the formation of a molecule of carbon dioxide CO2 , which occurs whenever a molecule of CO and an atom O are first neighbors adsorbed in the lattice. Since an oxygen atom or a molecule of CO are adsorbed into the lattice, they remain in the sites coming out only by reactions. We propose a catalytic system saturated by CO molecules in order to study the effect of temperature on the system and the oxidation of these species using the rules of the model ZGB with small modifications. Attractive interactions between adsorbed CO molecules and O atoms at the first neighboring sites and the desorption phenomenon were taken into consideration. We consider the interaction CO-CO more intense than O-O , so that the system energy is minimal when the entire lattice is filled by CO molecules and is maximum when the lattice is empty or filled totally or partially by not near-neighbors CO and O, being null its value for all these cases. We perform a random walk in the energy space bounded by the interval above, calculating the density of states by means of entropic simulations. Once the state density is obtained, we calculate the partition function and the thermodynamic properties for a given temperature range by means of the canonical average. We found, through of a finite-size scale analysis, that our system suffers a first-order phase transition.