Phase transitions in a two-dimensional lattice gas model of orientable diatomic molecules. II. Order-disorder transitions of superantiferromagnetic andc(2×2)AFphases

Abstract

The nature of phase transitions occurring in the two-dimensional spin-1 lattice model with the first-and second-nearest-neighbor interactions is studied using Monte Carlo methods. This system models the adsorption of rigid diatomic molecules ͑A-B͒ on ͑100͒ surfaces of crystals, assuming that each molecule is oriented perpendicularly to the crystal surface, and the binding energy depends on whether the A atom or B atom is adsorbed. It is shown that under the condition of a fully filled lattice, the order-disorder transition of the superantiferromagnetic ͑SAF͒ phase may occur via a continuous as well as a first-order phase transition, depending on the model parameters. The continuous order-disorder transition of the SAF phase is found to be nonuniversal. The nature of the various phase transitions is analyzed by the finite size scaling method. The application of this method is also demonstrated for the case of a second-order transition from one ordered phase to another ordered phase. We have also demonstrated that the phase diagram topology changes with the model parameters. While at low temperatures a first-order transition between the SAF phase and the c͑2 ϫ 2͒ AF -ordered phase corresponding to a half-filled lattice occurs, this transition line at higher temperatures may terminate either by a triple point or a tricritical point. For the latter case a phase diagram with a different type of multicritical point is suggested.

Structure of CO2 Adsorbed on the KCl(100) Surface

“…An exchange of electronic charge density with the surface can be neglected on alkali halides, deduced, e.g., from the analysis of the IR spectra of these adsorbates . There is some theoretical interest in such weakly bound two-dimensional molecular adsorbates: ,,,, compared to atom adsorption, the complexity increases due to the significance of orientational ordering. Electrostatic interaction, mainly of the dipole–dipole or quadrupole–quadrupole type, has the tendency to orient the molecules in domains with antiferroelectric or herringbone-like structures.…”

“…Electrostatic interaction, mainly of the dipole–dipole or quadrupole–quadrupole type, has the tendency to orient the molecules in domains with antiferroelectric or herringbone-like structures. Therefore, such systems serve also as model systems for studies of phase transitions between orientational order and disorder. , …”

Statistical Thermodynamics of Lattice Gas Models of Multisite Adsorption

“…Today there is a small number of papers devoted to theoretical investigation of the behavior of adsorption monolayer consisting of molecules that can have a different orientation with respect to the surface [88][89][90][91][92]. Let's examine them in detail.…”

“…There is the quite interesting model of spin-1 type, which can describe the adsorption of heteronuclear dimers on different lattices [91,92]. It is assumed in the model that all adsorbed molecules are oriented vertically to the surface only, and the energy of adsorption depends on what segment, A or B, molecule adsorb with.…”

“…It is assumed in the model that all adsorbed molecules are oriented vertically to the surface only, and the energy of adsorption depends on what segment, A or B, molecule adsorb with. The authors of [91,92] considered the various sets of lateral interactions between dimers, in particular, they took into account not only interactions between nearest neighbors, but also between next-nearest neighbors. Such complex lateral interactions in the system led to the set of ordered surface structures and phase transitions.…”