Reference hyper-netted chain: Difference between revisions

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(Note: the reference-HNC (RHNC) is sometimes referred to as the modified-HNC (MHNC) Ref.1).
The '''reference hyper-netted chain''' (RHNC) is sometimes referred to as the modified-HNC (MHNC) (Ref. 1)
Rosenfeld and Ashcroft (1979) (Ref. 1) proposed the `anzatz of universality':
Rosenfeld and Ashcroft (1979) (Ref. 1) proposed the `anzatz of universality':
  "...the bridge functions.. ..constitute the same family of curves, irrespective of the assumed pair potential"
  "...the bridge functions.. ..constitute the same family of curves, irrespective of the assumed pair potential"
The basis of the method is to solve the modified HNC equation
The basis of the method is to solve the modified [[HNC]] equation
(with inclusion of the one-parameter bridge functions
(with inclusion of the one-parameter [[bridge function]]s
appropriate to hard spheres), and determine the only free parameter <math>\eta</math>
appropriate to [[hard sphere model | hard spheres]]), and determine the only free parameter <math>\eta</math>
(related to the hard-sphere diameter) by requiring thermodynamic consistency.
(related to the hard-sphere diameter) by requiring [[thermodynamic consistency]].
Fred Lado  (Ref. 2) and Rosenfeld and Ashcroft (1979) (Ref. 3)
Fred Lado  (Ref. 2) and Rosenfeld and Ashcroft (1979) (Ref. 3)
noticed that the OZ equation can always be written in the form
noticed that the [[Ornstein-Zernike relation]]  can always be written in the form
:<math>\gamma_{12} =  \rho \int_V (h_{13} - \gamma_{13}) h_{23} ~{\rm d}(3)</math>
:<math>\gamma_{12} =  \rho \int_V (h_{13} - \gamma_{13}) h_{23} ~{\rm d}(3)</math>
In view of this a hybrid solution between the [[HNC| hyper-netted chain]]
In view of this a hybrid solution between the [[HNC| hyper-netted chain]]
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(See also Ref.s 6 and 7)
(See also Ref.s 6 and 7)
The RHNC closure is given by (Eq. 17 Ref. 7)
The RHNC closure is given by (Eq. 17 Ref. 7)
:<math> c\left(r\right) = h(r) - \ln [g(r) e^{\beta \phi(r)}] + B_0(r) </math>
:<math> c\left(r\right) = h(r) - \ln [g(r) e^{\beta \Phi(r)}] + B_0(r) </math>
along with the constraint (Eq. 18 Ref. 7)
along with the constraint (Eq. 18 Ref. 7)
:<math>\rho \int [g(r) - g_0(r)] \delta B_0(r) dr_3 = 0 </math>
:<math>\rho \int [g(r) - g_0(r)] \delta B_0(r) dr_3 = 0 </math>
Incorporating a reference potential <math>\phi_0(r)= \phi_0(r;\sigma,\epsilon)</math>
where <math>\Phi(r)</math> is the [[intermolecular pair potential]].
Incorporating a reference potential <math>\Phi_0(r)= \Phi_0(r;\sigma,\epsilon)</math>
this equation becomes  (Eqs. 19a and 19b in Ref. 7)
this equation becomes  (Eqs. 19a and 19b in Ref. 7)
:<math>\rho \int [g(r) - g_0(r)] \sigma \frac{\partial B_0(r)}{\partial \sigma}dr_3 = 0 </math>
:<math>\rho \int [g(r) - g_0(r)] \sigma \frac{\partial B_0(r)}{\partial \sigma}dr_3 = 0 </math>
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These are the conditions that will determine the optimum values of <math>\sigma</math> and <math>\epsilon</math>
These are the conditions that will determine the optimum values of <math>\sigma</math> and <math>\epsilon</math>
that minimise the free energy.  
that minimise the free energy.  
The RHNC satisfies the 'Hiroike' termodynamic relation test Ref. 7 and 8, i.e.
The RHNC satisfies the 'Hiroike' termodynamic relation test Ref. 7 and 9, i.e.
:<math>\left.\frac{\partial U}{\partial V}\right\vert_{T} = T \left.\frac{\partial p}{\partial T}\right\vert_{V} -p</math>
:<math>\left.\frac{\partial U}{\partial V}\right\vert_{T} = T \left.\frac{\partial p}{\partial T}\right\vert_{V} -p</math>
For highly asymmetric mixtures see Ref. 9.
For highly asymmetric mixtures see Ref. 9.
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==References==
==References==
#[http://dx.doi.org/10.1103/PhysRevA.20.1208 Yaakov Rosenfeld and N. W. Ashcroft "Theory of simple classical fluids: Universality in the short-range structure", Physical Review A '''20''' pp. 1208 - 1235 (1979)]
#[http://dx.doi.org/10.1103/PhysRevA.20.1208 Yaakov Rosenfeld and N. W. Ashcroft "Theory of simple classical fluids: Universality in the short-range structure", Physical Review A '''20''' pp. 1208 - 1235 (1979)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1103/PhysRevA.8.2548  F. Lado "Perturbation Correction for the Free Energy and Structure of Simple Fluids", Physical Review A    '''8''' 2548 - 2552 (1973)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1080/00268978700100441 Anatol Malijevský and Stanislav Labík "The bridge function for hard spheres", Molecular Physics, '''60''' pp. 663-669 (1987)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1080/00268978900101181 Stanislav Labík and Anatol Malijevský "Bridge function for hard spheres in high density and overlap regions", Molecular Physics, '''67''' pp. 431-438 (1989)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1016/0375-9601(82)90207-9  F. Lado  "A local thermodynamic criterion for the reference-hypernetted chain equation", Physics Letters A '''89''' pp. 196-198 (1982)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1103/PhysRevA.28.2374  F. Lado, S. M. Foiles and N. W. Ashcroft, "Solutions of the reference-hypernetted-chain equation with minimized free energy", Physical Review A '''28''' 2374 - 2379 (1983)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1143/JPSJ.12.326 Kazuo Hiroike "Radial Distribution Function of Fluids I", Journal of the Physical Society of Japan '''12''' pp. 326-334 (1957)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1143/JPSJ.12.864 Kazuo Hiroike "Radial Distribution Function of Fluids II", Journal of the Physical Society of Japan '''12''' pp. pp. 864-873 (1957)]
#[http://dx.doi.org/
#[http://dx.doi.org/10.1063/1.2102891    S. Amokrane, A. Ayadim, and J. G. Malherbe "Structure of highly asymmetric hard-sphere mixtures: An efficient closure of the Ornstein-Zernike equations", Journal of Chemical Physics, '''123''' 174508 (2005)]
#[http://dx.doi.org/
#[http://dx.doi.org/




#[PRA_1973_08_002548]
#[MP_1987_60_0663]
#[MP_1989_67_0431]
#[PLA_1982_89_0196]
#[PRA_1983_28_002374]
#[JPSJ_1957_12_00326]
#[JCP_2005_123_174508]


[[Category: Integral equations]]
[[Category: Integral equations]]

Latest revision as of 15:25, 15 April 2008

The reference hyper-netted chain (RHNC) is sometimes referred to as the modified-HNC (MHNC) (Ref. 1) Rosenfeld and Ashcroft (1979) (Ref. 1) proposed the `anzatz of universality':

"...the bridge functions.. ..constitute the same family of curves, irrespective of the assumed pair potential"

The basis of the method is to solve the modified HNC equation (with inclusion of the one-parameter bridge functions appropriate to hard spheres), and determine the only free parameter (related to the hard-sphere diameter) by requiring thermodynamic consistency. Fred Lado (Ref. 2) and Rosenfeld and Ashcroft (1979) (Ref. 3) noticed that the Ornstein-Zernike relation can always be written in the form

In view of this a hybrid solution between the hyper-netted chain approximation and the Malijevsky-Labik formula for hard spheres (Ref. 4 and 5) was proposed. The philosophy of this method is that the bridge functional of the liquid is fairly similar to that of the hard sphere fluid. (See also Ref.s 6 and 7) The RHNC closure is given by (Eq. 17 Ref. 7)

along with the constraint (Eq. 18 Ref. 7)

where is the intermolecular pair potential. Incorporating a reference potential this equation becomes (Eqs. 19a and 19b in Ref. 7)

and

These are the conditions that will determine the optimum values of and that minimise the free energy. The RHNC satisfies the 'Hiroike' termodynamic relation test Ref. 7 and 9, i.e.

For highly asymmetric mixtures see Ref. 9.

References[edit]

  1. Yaakov Rosenfeld and N. W. Ashcroft "Theory of simple classical fluids: Universality in the short-range structure", Physical Review A 20 pp. 1208 - 1235 (1979)
  2. F. Lado "Perturbation Correction for the Free Energy and Structure of Simple Fluids", Physical Review A 8 2548 - 2552 (1973)
  3. Anatol Malijevský and Stanislav Labík "The bridge function for hard spheres", Molecular Physics, 60 pp. 663-669 (1987)
  4. Stanislav Labík and Anatol Malijevský "Bridge function for hard spheres in high density and overlap regions", Molecular Physics, 67 pp. 431-438 (1989)
  5. F. Lado "A local thermodynamic criterion for the reference-hypernetted chain equation", Physics Letters A 89 pp. 196-198 (1982)
  6. F. Lado, S. M. Foiles and N. W. Ashcroft, "Solutions of the reference-hypernetted-chain equation with minimized free energy", Physical Review A 28 2374 - 2379 (1983)
  7. Kazuo Hiroike "Radial Distribution Function of Fluids I", Journal of the Physical Society of Japan 12 pp. 326-334 (1957)
  8. Kazuo Hiroike "Radial Distribution Function of Fluids II", Journal of the Physical Society of Japan 12 pp. pp. 864-873 (1957)
  9. S. Amokrane, A. Ayadim, and J. G. Malherbe "Structure of highly asymmetric hard-sphere mixtures: An efficient closure of the Ornstein-Zernike equations", Journal of Chemical Physics, 123 174508 (2005)