Dipolar Hard Sphere Fluid Research Articles

Structure of the dipolar hard sphere fluid near a neutral hard wall

The structure of a dipolar hard sphere fluid near a neutral hard wall is calculated using a diagrammatic expansion which has been recently proposed. The isotropic part of the profile is different from the hard sphere profile only in the vicinity of the wall. A layering effect in the orientational structure is predicted. Near the wall the orientation parallel to the wall is favoured. The calculated profiles compare well with the Monte Carlo results recently obtained by D. Levesque and J. J. Weis.

The solution of the hypernetted-chain approximation for fluids of nonspherical particles. A general method with application to dipolar hard spheres

In this paper we describe a general method for the numerical solution of the full hypernetted-chain (HNC) theory for fluids characterized by angle-dependent pair potentials. This method is also applicable to the closely related reference hypernetted-chain (RHNC) approximation. The only formal restriction is that the pair potential and correlation functions must be expandable in a basis set of rotational invariants. We present explicit numerical solutions of the RHNC theory for dense dipolar hard sphere fluids and detailed comparisons are made with previous theories and computer simulation results. It is found that the full RHNC theory generally improves upon the previous reference linearized and quadratic HNC approximations. The values given by the RHNC theory for the static dielectric constants are smaller than those given by these earlier approximations and are in much better agreement with computer simulations.

Structure of the dipolar hard sphere fluid near a hard wall

Two new approximations are proposed for the profile of the dipolar hard sphere fluid near a wall. In the scheme of the optimized cluster theory we give an expression which includes a quadratic dependence on the renormalized potential of the homogeneous fluid. From the classical grand canonical ensemble we give a λ expansion. These two approaches go beyond the MSA, give a profile which depends on the magnitude of the dipole moment and show that some orientations are favoured in the liquid. At low density the profile has a very long tail and the orientational effect comes from the image potential. However, the surface potential still vanishes while the contact value is changed.

An effective pair potential for dipolar fluids

The possibility of representing the orientational correlations in a dipolar fluid by an effective pair potential, U eff(r), depending only on the separation r, is considered. U eff(r) is obtained from the two-particle orientational partition function by series expansion and direct numerical integration methods for a wide range of interaction strengths. Free energies are obtained for the dipolar hard sphere fluid by use of the GvdW theory of simple fluids and compared with Monte Carlo simulation results. The coexistence curve is also obtained and compared with Monte Carlo, Pade and MSA results. The critical temperature is overestimated by about 30 per cent but the critical volume agrees well with the simulation estimate.

Application of perturbation theory to the calculation of the dielectric constant of a dipolar hard sphere fluid

Perturbation theory is applied to calculate the dielectric constant of a dipolar hard sphere fluid. The results seem to be fairly good. However, this conclusion can only be stated tentatively because of uncertainties in the computer simulation estimates of the dielectric constant of this fluid.

Perturbation theory of dipolar hard spheres: The vapour-liquid equilibrium of strongly polar mixtures

Winkelmann, J., 1983. Perturbation theory of dipolar hard spheres: the vapour-liquid equilibrium of strongly polar mixtures. Fluid Phase Equilibria 11: 207-224.Thermodynamic perturbation theory has been applied to calculate vapour-liquid equilibria (VLE) for binary mixtures of polarizable, dipolar hard-sphere fluids. Effective potential parameters determined previously from the vapour pressures of pure compounds are used to represent the intermolecular interactions in strongly polar and associating fluids. The one-fluid conformal-solution approach is adopted.With a binary correction factor k12 the theory is found able to predict VLE over wide ranges of temperature and pressure. A similar procedure yields a calculated azeotropic line. In the case of hydrogen-bond formation, a temperature-dependent k12 reproduces both GE and HE at various temperatures and results in a rather exact azeotropic line.

The third dielectric and pressure virial coefficients of dipolar hard sphere fluids

Approximate analytic expressions are generated for the third dielectric virial coefficient C e*, and the third pressure virial coefficient C p*, of a fluid of hard sphere dipoles.

Perturbation theory of dipolar hard spheres: The vapour—liquid equilibrium of strongly polar substances

Thermodynamic perturbation theory is applied to a fluid of polarizable dipolar hard spheres. Calculations of vapour—liquid equilibrium (VLE) are carried out and the vapour pressure, heat of vaporization and the densities of both coexisting phases are obtained. The inverse procedure allows the determination of effective potential parameters by fitting some experimental vapour pressure data. Using these parameters the thermodynamic properties of the VLE can be extrapolated to temperatures close to the critical point. For some strongly polar substances an excellent agreement between the predicted vapour pressure and the experimental results was found. Thus the perturbation theory provides a very successful procedure for predicting vapour pressures over a wide range of temperature.

A Monte Carlo study of the dense polarizable dipolar hard sphere fluid

In this paper we report Monte Carlo results for a fluid of polarizable dipolar hard spheres. Both isotropic and anisotropic particles are considered. It is shown that the induced forces make a large contribution to the thermodynamic properties and significantly influence the fluid structure. The various approximate treatments of polarizable systems are evaluated and a recent theory proposed by Wertheim is found to be very successful.

Perturbation theory for the radial distribution functions of dipolar and quadrupolar hard-sphere fluids

The radial distribution functions for the dipolar and the quadrupolar hard-sphere fluids are calculated by means of statistical-mechanical perturbation theory to third order using the hypernetted-chain (HNC) theory to approximate the perturbation terms. For both fluids the perturbation expansions through third order disagree with computer simulations, indicating that the expansion converges slowly. On the other hand, a Pade approximant, constructed from the second and third-order HNC terms, for each radial distribution function agrees excellently with the computer simulations.

Perturbation theory and the radial distribution function of fluids with nonspherical potentials

A perturbation expansion for the radial distribution function of fluids with nonspherical pair potentials is discussed. Numerical calculations are presented for dipolar hard-sphere and quadrupolar hard-sphere fluids. Agreement with the computer simulation results is excellent, even at high dipole and quadrupole moments.