The analytic method for deriving the equation of state of a cell fluid model in the region above the critical temperature (T T c ) is elaborated using the renormalization group transformation in the collective variables set.Mathematical description with allowance for non-Gaussian fluctuations of the order parameter is performed in the vicinity of the critical point on the basis of the ρ 4 model. The proposed method of calculation of the grand partition function allows one to obtain the equation for the critical temperature of the fluid model in addition to universal quantities such as critical exponents of the correlation length. The isothermal compressibility is plotted as a function of density. The line of extrema of the compressibility in the supercritical region is also represented.

This article embraces a theoretical description of the first order phase transition in liquid metals with application of a cell fluid model. The results are obtained through calculation of the grand partition function without usage of phenomenological parameters. The Morse potential is used for calculation of the equation of state and the coexistence curve. Specific results for sodium and potassium are obtained. Comparison of outcome of analytical expressions with data of computer simulations is presented. PACs: 51.30.+i, 64.60.fd

The method to calculate the grand partition function of a particle system, in which constituents interact with each other via potential, that include repulsive and attractive components, is proposed. The cell model, which was introduced to describe critical phenomena and phase transitions, is used to provide calculations. The exact procedure of integration over particle coordinates and summation over number of particles is proposed. As a result, an evident expression for the grand partition function of the fluid cell model is obtained in the form of multiple integral over collective variables. As it can be seen directly from the structure of the transition jacobian, the present multiparticle model appeared to be different from the Ising model, which is widely used to describe fluid systems. The state equation, which is valid for wide temperature ranges both above and below the critical one, is derived in mean-field approximation. The pressure calculated for the cell model at temperatures above the critical one is found to be continuously increasing function of temperature and density. The isotherms of pressure as a function of density have horizontal parts at temperatures below the critical one.

We propose a method of describing a phase transition in a cell fluid model with pair interaction potential that includes repulsive and attractive parts. An exact representation of the grand partition function of this model is obtained in the collective variables set. The behavior of the system at temperatures below and above the critical one is explored in the approximation of a mean-field type. An explicit analytic form of the equation of state which is applicable in a wide range of temperatures is derived, taking into account an equation between chemical potential and density. The coexistence curve, the surface of the equation of state and the phase diagram of the cell Morse fluid are plotted.

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The present article gives a theoretical description of a first-order phase transition in the cell fluid model with a modified Morse potential and an additional repulsive interaction. In the framework of the grand canonical ensemble, the equation of state of the system in terms of chemical potential–temperature and terms of density–temperature is calculated for a wide range of the density and temperature. The behavior of the chemical potential as a function of the temperature and density is investigated. The maximum and minimum admissible values of the chemical potential, which approach each other with decreasing the temperature, are exhibited. The existence of a liquid-gas phase transition in a limited temperature range below the critical Tc is established.

The present manuscript gives a theoretical description of the first-order phase transition in a cell fluid model with a modified Morse potential and additional repulsive interaction. In the framework of the grand canonical ensemble, the equation of state of the system in terms of chemical potential-temperature and terms of densitytemperature is calculated for a wide range of density and temperature. The behaviour of the chemical potential as a function of temperature and density is investigated. The maximum and minimum admissible values of the chemical potential, which approach each other with decreasing temperature, are exhibited. The existence of a liquid-gas phase transition in a limited temperature range below the critical T c is established.

The calculation method of the grand partition function of a simple fluid model in the frame of a generalized lattice model, where each cell may contain a random number of particles, is proposed. As an interaction potential between particles, the Morse potential is chosen. In vcourse of calculations, the summation over the number of particles and the integration over their coordinates are performed. Using the simplest approximation, the equation of state valid in a wide temperature range is obtained. At temperatures lower than the critical one, the presence of horizontal plots on the pressure vs density curve is found.