Two-component Lattice-gas Model Research Articles

Magnetization process and low-temperature thermodynamics of a spin-1/2 Heisenberg octahedral chain

Low-temperature magnetization curves and thermodynamics of a spin-1/2 Heisenberg octahedral chain with the intra-plaquette and monomer-plaquette interactions are examined within a two-component lattice-gas model of hard-core monomers, which takes into account all low-lying energy modes in a highly frustrated parameter space involving the monomer-tetramer, localized many-magnon and fully polarized ground states. It is shown that the developed lattice-gas model satisfactorily describes all pronounced features of the low-temperature magnetization process and the magneto-thermodynamics such as abrupt changes of the isothermal magnetization curves, a double-peak structure of the specific heat or a giant magnetocaloric effect.

Underpotential deposition of Cu on Au(111) in sulfate-containing electrolytes: A theoretical and experimental study

We study the underpotential deposition of Cu on single-crystal Au(111) electrodes in sulfate-containing electrolytes by a combination of computational statistical-mechanics based lattice-gas modeling and experiments. The experimental methods are in situ cyclic voltammetry and coulometry and ex situ Auger electron spectroscopy and low-energy electron diffraction. The experimentally obtained voltammetric current and charge densities and adsorbate coverages are compared with the predictions of a two-component lattice-gas model for the coadsorption of Cu and sulfate. This model includes effective, lateral interactions out to fourth-nearest neighbors. Using group-theoretical ground-state calculations and Monte Carlo simulations, we estimate effective electrovalences and lateral adsorbate–adsorbate interactions so as to obtain overall agreement with experiments, including both our own and those of other groups. In agreement with earlier work, we find a mixed (√3×√3) phase consisting of 2/3 monolayer Cu and 1/3 monolayer sulfate at intermediate electrode potentials, delimited by phase transitions at both higher and lower potentials. Our approach provides estimates of the effective electrovalences and lateral interaction energies, which cannot yet be calculated by first-principles methods.

Two-component lattice-gas model for surface segregation in liquid alloys.

Using a two-component lattice-gas model in a mean-field approximation, we calculate the surface tension and surface concentration of a model liquid alloy as a function of temperature and concentration. When the alloy has a negative heat of mixing (that is, has a tendency to phase separate), the concentration of the low-surface-tension component is much larger on the surface than in the bulk. This surface segregation decreases with increasing temperature, leading to a strongly negative surface entropy at small impurity concentrations and sufficiently low temperatures. The results are in agreement with an earlier density-functional calculation on ${\mathrm{Na}}_{\mathrm{x}}$${\mathrm{K}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ as well as with experiments on ${\mathrm{Ga}}_{\mathrm{x}}$${\mathrm{Sn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$. .AE

Mean-field lattice gas description of vapour-liquid and supercritical equilibria

Recently we improved the mean-field two-component lattice-gas model introducing interacting surface areas and an empirical entropy of mixing parameter. The treatment in its present form has proven to be well capable of describing almost quantitatively fluid-phase behaviour of non-polar and polar substances of low- and high molar mass and mixtures thereof in large temperature and pressure ranges. The model works particularly well in the critical fluid region which allows adjustment of the parameters to scarce experimental data with expressions for spinodal, critical condition and equation of state.

Critical phenomena in a binary lattice gas. II. Series analysis

The critical behavior of a two-component lattice-gas model (the 1-2 model) in two and three dimensions is investigated by means of standard and nonstandard methods of series analysis on exact series expansions for the thermodynamic properties of the model. The model exhibits a critical line that passes from the Ising critical point at finite temperature to a critical point at zero temperature. In two dimensions the Ising values of the critical exponents found along the critical line and at zero temperature support the expectation that the model lies in the Ising universality class. In three dimensions Ising values of the critical exponents are found away from zero temperature, but near and at zero temperature the series analysis suggests a crossover to non-Ising values of the critical exponents. This would imply that the model belongs to the Ising universality class at nonzero temperatures and to a different universality class at zero temperature\char22{}a quite unexpected result. Various possible explanations for this unusual behavior of the series results are discussed.

Two-component lattice-gas model with a liquid–vapor phase transition in both pure components

A two-component decorated lattice-gas model is presented that possesses a liquid–vapor phase transition in both pure components with a coexistence surface and critical curve which extend smoothly from one pure component to the other. The model is exactly soluble in terms of the simple one-component lattice gas of Yang and Lee (spin-1/2 Ising model) and exhibits nonclassical critical exponents. It can produce azeotropy and critical azeotropic points, and is used to analyze the vicinity of the critical azeotrope. For sufficiently repulsive interactions between primary and secondary cell occupants the model exhibits multiple phase transitions and a phenomenon analogous to saddle-point azeotropy.

The two-component lattice-gas model

In this article a description is presented of the two-component lattice-gas model. This model combines the essential features of the lattice theory of Guggenheim for a two-component system and the lattice-gas model for a one-component system. Computer calculations of the critical lines and the spinodal curves have been performed for various combinations of the energy parameters. The coordinates of the double plait points have been determined analytically.

Gas—gas equilibrium and the two-component lattice-gas model

A two-component lattice-gas model is developed to explain the phase equilibria in binary systems.