Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-10ADSORPTION OF COMPLEX MOLECULES WITH DIFFERENTORIENTATION IN MONOLAYER ON SQUARE LATTICE.MONTE CARLO AND TRANSFER-MATRIX TECHNIQUESV.F. Fefelov*, V.A. Gorbunov*, A.V. Myshlyavtsev* , **, M.D. Myshlyavtseva**Omsk State Technical University, Omsk, Russia**Institute of Hydrocarbons Processing SB RAS, Omsk, RussiaThe most of the studies of adsorption are devoted to the monomolecular adsorption, butthe statistics and thermodynamics of multisite one is the interesting problem to date. Thissituation is mainly associated to three difficulties which make the complex moleculesstatistics different from the usual single particle statistics [1]. Namely, 1) no statisticalequivalence exists between particles and vacancies, 2) the occupation of a given lattice siteensures that at least one of its nearest-neighbor sites is occupied, and 3) an isolated vacancycannot serve to determining whether that site can ever become occupied. Moreover, there is aproblem of different molecular orientation in adlayer [2]. The aim of this study isinvestigation of complex molecules adsorption on square lattice with different molecularorientations in adlayer.To describe adsorption of complex molecules on homogenous surfaces we used thegeneral lattice gas model. One of the simplest kinds (do not taking into account the dimeradsorption) of complex molecules which can variously orientate on the surface isquadrangular pyramid. Such molecules can adsorb by two different ways: 1) adsorbedmolecule occupies one site (on top adsorption); 2) adsorbed molecule occupies four sites (onfacet adsorption).To take into account own size of the molecules we involve infinity strong repulsiveinteractions between nearest-neighbor particles (adsorption to nearest-neighbor sites aroundadsorbed molecules is prohibited). The model was studied with grand canonical ensemble.The model parameters are chemical potential μ, temperature T and ∆ – difference between theadsorption heat on facet and on top adsorption.One of the methods used for calculations was transfer-matrix technique. The transfermatrixis generated for stripe cut out from the square lattice with M sites along X axis andwith infinity length along Y axis. Along X axis periodic boundary conditions are used. Forour model the state of the surface in whole can be described as set of lattice site states, eachones can be in six states. On the other hand, we used the standard Monte Carlo method. Thesites were arranged in a square lattice of side L (N=L×L), with conventional periodicboundary conditions. With this method phase diagram was made.The multiple-histogram reweighting and finite-size scaling techniques (the fourth-orderBinder’s cumulant of the order parameter) have been used to estimate the phase diagram of44