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(Note: the reference-HNC (RHNC) is somtimes referred to as the modified-HNC (MHNC) \cite{PRA_1979_20_001208}). | |||
Rosenfeld and Ashcroft (1979) | Rosenfeld and Ashcroft (1979) \cite{PRA_1979_20_001208} | ||
proposed the `anzatz of universality': | |||
The basis of the method is to solve the modified | {\it ``...the bridge functions.. ..constitute the same family of curves, irrespective of the assumed pair potential".} | ||
(with inclusion of the one-parameter | The basis of the method is to solve the modified HNC equation | ||
appropriate to | (with inclusion of the one-parameter bridge functions | ||
(related to the hard-sphere diameter) by requiring | appropriate to hard spheres), and determine the only free parameter $\eta$ | ||
Fred Lado | (related to the hard-sphere diameter) by requiring thermodynamic consistency.\\ | ||
noticed that the | Fred Lado \cite{PRA_1973_08_002548} and Rosenfeld and Ashcroft (1979) \cite{PRA_1979_20_001208} | ||
noticed that the OZ equation can always be written in the form | |||
In view of this a hybrid solution between the | \begin{equation} | ||
approximation and the Malijevsky-Labik formula for hard spheres | \gamma_{12} = \rho \int_V (h_{13} - \gamma_{13}) h_{23} ~{\rm d}(3) | ||
was proposed. The philosophy of this method is that the bridge functional of the | \end{equation} | ||
liquid is fairly similar to that of the hard sphere fluid. | In view of this a hybrid solution between the HNC | ||
approximation and the Malijevsky-Labik formula for hard spheres \cite{MP_1987_60_0663,MP_1989_67_0431} | |||
The RHNC closure is given by (Eq. 17 | was proposed.\\ | ||
The philosophy of this method is that the bridge functional of the | |||
along with the constraint (Eq. 18 | liquid is fairly similar to that of the | ||
hard sphere fluid. | |||
See also \cite{PLA_1982_89_0196,PRA_1983_28_002374}.\\ | |||
Incorporating a reference potential | The RHNC closure is given by (Eq. 17 \cite{PRA_1983_28_002374}) | ||
this equation becomes (Eqs. 19a and 19b | \begin{equation} | ||
c(r) = h(r) - \ln [g(r) e^{\beta \phi(r)}] + B_0(r) | |||
\end{equation} | |||
along with the constraint (Eq. 18 \cite{PRA_1983_28_002374}) | |||
\begin{equation} | |||
\rho \int [g(r) - g_0(r)] \delta B_0(r) {\rm d}{\bf r}_3 = 0 | |||
\end{equation} | |||
Incorporating a reference potential $\phi_0(r)= \phi_0(r;\sigma,\epsilon)$ | |||
this equation becomes (Eqs. 19a and 19b \cite{PRA_1983_28_002374}) | |||
\begin{equation} | |||
\rho \int [g(r) - g_0(r)] \sigma \frac{\partial B_0(r)}{\partial \sigma} {\rm d}{\bf r}_3 = 0 | |||
\end{equation} | |||
and | and | ||
\begin{equation} | |||
These are the conditions that will determine the optimum values of | \rho \int [g(r) - g_0(r)] \epsilon \frac{\partial B_0(r)}{\partial \epsilon} {\rm d}{\bf r}_3 = 0 | ||
that minimise the free energy. | \end{equation} | ||
The RHNC satisfies the 'Hiroike' termodynamic relation test | These are the conditions that will determine the optimum values of | ||
$\sigma$ and $\epsilon$ that minimise the free energy. | |||
For highly asymmetric mixtures see | The RHNC satisfies the 'Hiroike' termodynamic relation test \cite{PRA_1983_28_002374,JPSJ_1957_12_00326}, i.e. | ||
\begin{equation} | |||
\left.\frac{\partial U}{\partial V}\right\vert_{T} = T \left.\frac{\partial p}{\partial T}\right\vert_{V} -p | |||
\end{equation} | |||
For highly asymmetric mixtures see \cite{JCP_2005_123_174508}. | |||
==References== | ==References== | ||