Hard-core Yukawa Fluid Research Articles

An analytical equation of state for the hard-core Yukawa fluid

An analytical equation of state for the hard-core Yukawa fluid

An analytical equation of state for the hard-core Yukawa fluid

An analytic equation of state for the hard core Yukawa fluid is presented. This explicit, nonempirical equation of state is based on the inverse temperature expansion of the free energy from the mean-spherical approximation (MSA). This equation of state yields an excellent description of the pressure when compared with simulation results. The critical point properties obtained using this equation of state are almost identical to those obtained from the exact MSA. The vapour-liquid coexistence is also studied; the resulting phase diagram agrees very well with the result from the Gibbs ensemble simulation, except in the vicinity of the critical point.

Phase diagram for the Lennard-Jones fluid modelled by the hard-core Yukawa fluid

The liquid-gas phase diagram for the Lennard-Jones (LJ) fluid model is obtained using the mean spherical approximation (MSA) for the corresponding hard-core Yukawa fluid. The calculated phase diagram is compared with the phase diagrams for the LJ fluid predicted by the Gibbs ensemble Monte Carlo simulation, and by the Percus-Yevick (PY) and reference hypernetted chain (RHNC) theories. The accuracy of the MSA is comparable with the accuracy of the PY approximation. Although the MSA is less accurate than the RHNC approximation, it has an important advantage of being solvable along the whole liquid-gas coexistence curve, including the vicinity of the critical point.

RESEARCH NOTE Phase diagram for the Lennard-Jones fluid modelled by the hard-core Yukawa fluid

RESEARCH NOTE Phase diagram for the Lennard-Jones fluid modelled by the hard-core Yukawa fluid

Phase diagram for the dimerizing hard-core Yukawa fluid

The liquid-gas phase diagram for the dimerizing hard-core Yukawa fluid is calculated. The model consists of the one-site hard-sphere dimerizing model of Wertheim with an additional Yukawa attraction included into the nonassociating part of the interaction. The thermodynamic properties of the model are obtained from the analytical solution of the associative mean spherical approximation. Predictions of the theory are consistent with qualitative trends in the behaviour of the phase equilibrium of associating liquids.

The structure of an associating hard core Yukawa fluid near a hard wall

An investigation is begun into the structure of a chemically reacting or associating hard core Yukawa fluid near a hard wall by using Monte Carlo simulations. The model of the interparticle potential is an extension of that introduced by Cummings and Stell for an overlappping hard sphere fluid. This investigation studies the changes in the structure of this chemically reacting fluid at the wall, introduced by the presence of long-range attractive forces acting between atoms. The long-range attractive forces cause a lowering of the total number of particles in the vicinity of the wall and weaken the orientational ordering of the dimers formed by the effect of the chemical interactions. Also the singlet integral equation approach is applied to calculate the density profiles. A comparison of the theoretical predictions with the Monte Carlo data indicates that, in contrast to systems without long-range attractive forces, the singlet theory is insufficient, especially when the chemical interactions increase.

Microscopic theoretical determination of the phase diagram of the hard core Yukawa fluid

The binodal and the freezing line of the hard core Yukawa fluid (HCYF) are determined by using modified hypernetted chain (MHNC) theory and the so-called HMSA theory. The results are compared with available simulation data and density functional theory (DFT). Agreement with simulation is generally satisfactory and quantitative for the MHNC binodal line. Agreement with the DFT freezing line is also satisfactory. On the basis of these results an estimate is possible of the critical and triple point parameters of the HCYF. Possible extensions of the present approach to other simple model fluids are discussed.

Vapour-liquid equilibria of the hard core Yukawa fluid

Techniques which extend the range of applicability of the Gibbs ensemble technique for particles which interact with a hard core potential are described. The power of the new technique is demonstrated in a numerical study of the vapour-liquid coexistence curve of the hard core Yukawa fluid.

Density functional theory of the freezing of the hard-core Yukawa fluid

The freezing of a hard-core fluid with repulsive Yukawa interactions is systematically investigated for various values of the screening constant, using density functional theory.

Analytical formulation of the optimized-random-phase-approximation for a hard-core Yukawa fluid

A method for analytical calculation of thermodynamic functions (the internal energy, free energy, chemical potential, energy and virial pressure, compressibility) for a hard-core Yukawa fluid (HCYF) in the optimized random phase approximation (ORPA) is presented. The method makes use of the analytical solution of the Ornstein-Zernike equation with a hard-core condition and the direct correlation function of two-Yukawa-function form. One Yukawa function is related to the interaction potential whereas the second one serves to obtain the generalized mean spherical approximation form of the hard-sphere direct correlation function. All thermodynamic quantities are analytical functions of the six parameters γ1, γ2, d 1, a and b whose values may be easily found with the use of an existing efficient algorithm. When the hard-sphere system is described in the Percus-Yevick approximation then the derived formulae reduce to the analytical mean-spherical-approximation (MSA) expressions derived by Høye and Stell. If the properties of the HCYF are evaluated in the ORPA then the first order quantum correction to the classical value of the free energy is also an analytical function of these parameters. The ORPA results for the internal energy and pressure are close to the Monte Carlo data and they are slightly better than the MSA and Barker and Henderson (BH) perturbation theory results. The ORPA free energies are always lower than the MSA or BH results although the differences between them are small.

Freezing of the hard core Yukawa fluid

We have studied the freezing of hard spheres with a Yukawa attractive or repulsive potential in the mean spherical approximation by using the density functional theory proposed by Ramakrishnan and Yussouff and extended later by Haymet and Oxtoby. We have calculated the densities of the liquid and solid phases at the phase transition as a function of temperature for two different parameters of the range of Yukawa potential (z=1 and z=5).