<?xml version="1.0"?>
<feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en">
	<id>http://www.sklogwiki.org/SklogWiki/api.php?action=feedcontributions&amp;feedformat=atom&amp;user=146.155.46.185</id>
	<title>SklogWiki - User contributions [en]</title>
	<link rel="self" type="application/atom+xml" href="http://www.sklogwiki.org/SklogWiki/api.php?action=feedcontributions&amp;feedformat=atom&amp;user=146.155.46.185"/>
	<link rel="alternate" type="text/html" href="http://www.sklogwiki.org/SklogWiki/index.php/Special:Contributions/146.155.46.185"/>
	<updated>2026-04-30T22:22:07Z</updated>
	<subtitle>User contributions</subtitle>
	<generator>MediaWiki 1.41.0</generator>
	<entry>
		<id>http://www.sklogwiki.org/SklogWiki/index.php?title=Lennard-Jones_model&amp;diff=14118</id>
		<title>Lennard-Jones model</title>
		<link rel="alternate" type="text/html" href="http://www.sklogwiki.org/SklogWiki/index.php?title=Lennard-Jones_model&amp;diff=14118"/>
		<updated>2014-04-01T19:43:33Z</updated>

		<summary type="html">&lt;p&gt;146.155.46.185: /* n-m García Verdugo potential */&lt;/p&gt;
&lt;hr /&gt;
&lt;div&gt;The &#039;&#039;&#039;Lennard-Jones&#039;&#039;&#039; [[intermolecular pair potential]] is a special case of the [[Mie potential]] and takes its name from  [[ Sir John Edward Lennard-Jones KBE, FRS | Sir John Edward Lennard-Jones]] &lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1098/rspa.1924.0081  John Edward Lennard-Jones &amp;quot;On the Determination of Molecular Fields. I. From the Variation of the Viscosity of a Gas with Temperature&amp;quot;, 	Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character &#039;&#039;&#039;106&#039;&#039;&#039; pp. 	441-462 (1924)] &amp;amp;sect; 8 (ii)&amp;lt;/ref&amp;gt; &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1098/rspa.1924.0082 John Edward Lennard-Jones &amp;quot;On the Determination of Molecular Fields. II. From the Equation of State of a Gas&amp;quot;,  Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character &#039;&#039;&#039;106&#039;&#039;&#039; pp. 463-477 (1924)] Eq. 2.05&amp;lt;/ref&amp;gt;.&lt;br /&gt;
The Lennard-Jones [[models |model]] consists of two &#039;parts&#039;; a steep repulsive term, and&lt;br /&gt;
smoother attractive term, representing the London dispersion forces &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1007/BF01421741 F. London &amp;quot;Zur Theorie und Systematik der Molekularkräfte&amp;quot;, Zeitschrift für Physik A Hadrons and Nuclei &#039;&#039;&#039;63&#039;&#039;&#039; pp. 245-279 (1930)]&amp;lt;/ref&amp;gt;. Apart from being an important model in itself,&lt;br /&gt;
the Lennard-Jones potential frequently forms one of &#039;building blocks&#039; of many [[force fields]]. It is worth mentioning that the 12-6 Lennard-Jones model is not the &lt;br /&gt;
most faithful representation of the potential energy surface, but rather its use is widespread due to its computational expediency.&lt;br /&gt;
For example, the repulsive term is maybe better described with the [[exp-6 potential]].&lt;br /&gt;
One of the first [[Computer simulation techniques |computer simulations]] using the Lennard-Jones model was undertaken by Wood and Parker in 1957 &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.1743822 W. W. Wood and F. R. Parker &amp;quot;Monte Carlo Equation of State of Molecules Interacting with the Lennard‐Jones Potential. I. A Supercritical Isotherm at about Twice the Critical Temperature&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;27&#039;&#039;&#039; pp. 720- (1957)]&amp;lt;/ref&amp;gt; in a  study of liquid [[argon]].&lt;br /&gt;
&lt;br /&gt;
== Functional form == &lt;br /&gt;
The Lennard-Jones potential is given by&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt; \Phi_{12}(r) = 4 \epsilon \left[ \left(\frac{\sigma}{r} \right)^{12}-  \left( \frac{\sigma}{r}\right)^6 \right] &amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
or is sometimes expressed as &lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt; \Phi_{12}(r) = \frac{A}{r^{12}}-  \frac{B}{r^6}&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
where&lt;br /&gt;
* &amp;lt;math&amp;gt;r := |\mathbf{r}_1 - \mathbf{r}_2|&amp;lt;/math&amp;gt;&lt;br /&gt;
* &amp;lt;math&amp;gt; \Phi_{12}(r) &amp;lt;/math&amp;gt; is the [[intermolecular pair potential]] between two particles or &#039;&#039;sites&#039;&#039;&lt;br /&gt;
* &amp;lt;math&amp;gt; \sigma &amp;lt;/math&amp;gt; is the value of &amp;lt;math&amp;gt;r&amp;lt;/math&amp;gt; at which &amp;lt;math&amp;gt; \Phi_{12}(r)=0&amp;lt;/math&amp;gt;&lt;br /&gt;
* &amp;lt;math&amp;gt; \epsilon &amp;lt;/math&amp;gt; is the well depth (energy)&lt;br /&gt;
* &amp;lt;math&amp;gt;A= 4\epsilon \sigma^{12}&amp;lt;/math&amp;gt;, &amp;lt;math&amp;gt;B= 4\epsilon \sigma^{6}&amp;lt;/math&amp;gt;&lt;br /&gt;
* Minimum value of &amp;lt;math&amp;gt; \Phi_{12}(r) &amp;lt;/math&amp;gt; at &amp;lt;math&amp;gt; r = r_{min} &amp;lt;/math&amp;gt;;  &lt;br /&gt;
: &amp;lt;math&amp;gt; \frac{r_{min}}{\sigma} = 2^{1/6} \simeq   1.12246 ...  &amp;lt;/math&amp;gt;&lt;br /&gt;
In reduced units: &lt;br /&gt;
* Density: &amp;lt;math&amp;gt; \rho^* := \rho \sigma^3 &amp;lt;/math&amp;gt;&lt;br /&gt;
where &amp;lt;math&amp;gt; \rho := N/V &amp;lt;/math&amp;gt; (number of particles &amp;lt;math&amp;gt; N &amp;lt;/math&amp;gt; divided by the volume &amp;lt;math&amp;gt; V &amp;lt;/math&amp;gt;)&lt;br /&gt;
* Temperature: &amp;lt;math&amp;gt; T^* := k_B T/\epsilon &amp;lt;/math&amp;gt;&lt;br /&gt;
where &amp;lt;math&amp;gt; T &amp;lt;/math&amp;gt;  is the absolute [[temperature]] and &amp;lt;math&amp;gt; k_B &amp;lt;/math&amp;gt; is the [[Boltzmann constant]]&lt;br /&gt;
&lt;br /&gt;
The following is a plot of the Lennard-Jones model for the Rowley, Nicholson and Parsonage parameter set &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1016/0021-9991(75)90042-X   L. A. Rowley, D. Nicholson and N. G. Parsonage &amp;quot;Monte Carlo grand canonical ensemble calculation in a gas-liquid transition region for 12-6 Argon&amp;quot;, Journal of Computational Physics  &#039;&#039;&#039;17&#039;&#039;&#039; pp. 401-414 (1975)]&amp;lt;/ref&amp;gt; (&amp;lt;math&amp;gt;\epsilon/k_B = &amp;lt;/math&amp;gt; 119.8 K and &amp;lt;math&amp;gt;\sigma=&amp;lt;/math&amp;gt; 0.3405 nm). See [[argon]] for other parameter sets.&amp;lt;br&amp;gt;&lt;br /&gt;
[[Image:Lennard-Jones.png|500px]]&lt;br /&gt;
==Critical point==&lt;br /&gt;
The location of the [[Critical points |critical point]] is &lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.477099  J. M. Caillol &amp;quot; Critical-point of the Lennard-Jones fluid: A finite-size scaling study&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;109&#039;&#039;&#039; pp. 4885-4893 (1998)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
:&amp;lt;math&amp;gt;T_c^* = 1.326 \pm 0.002&amp;lt;/math&amp;gt;&lt;br /&gt;
at a reduced density of&lt;br /&gt;
:&amp;lt;math&amp;gt;\rho_c^* = 0.316 \pm 0.002&amp;lt;/math&amp;gt;&lt;br /&gt;
The critical [[compressibility factor]] is given by &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.4829837 V. L. Kulinskii &amp;quot;The critical compressibility factor of fluids from the global isomorphism approach&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;139&#039;&#039;&#039; 184119 (2013)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;Z_c = \frac{p_cv_c}{RT_c} = 0.281&amp;lt;/math&amp;gt; &lt;br /&gt;
&lt;br /&gt;
Vliegenthart and Lekkerkerker&lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.481106 G. A. Vliegenthart and H. N. W. Lekkerkerker &amp;quot;Predicting the gas–liquid critical point from the second virial coefficient&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;112&#039;&#039;&#039; pp. 5364-5369 (2000)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.3496468  L. A. Bulavin  and V. L. Kulinskii &amp;quot;Generalized principle of corresponding states and the scale invariant mean-field approach&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;&#039;133&#039;&#039;&#039; 134101 (2010)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
have suggested that the critical point is related to the [[second virial coefficient]] via the expression &lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;B_2 \vert_{T=T_c}= -\pi \sigma^3&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
==Triple point==&lt;br /&gt;
The location of the [[triple point]] as found by Mastny and  de Pablo &amp;lt;ref name=&amp;quot;Mastny&amp;quot;&amp;gt; [http://dx.doi.org/10.1063/1.2753149     Ethan A. Mastny and Juan J. de Pablo &amp;quot;Melting line of the Lennard-Jones system, infinite size, and full potential&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;127&#039;&#039;&#039; 104504 (2007)]&amp;lt;/ref&amp;gt; is&lt;br /&gt;
:&amp;lt;math&amp;gt;T_{tp}^* = 0.694&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;\rho_{tp}^* = 0.84&amp;lt;/math&amp;gt; (liquid); &lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;\rho_{tp}^* = 0.96&amp;lt;/math&amp;gt; (solid).&lt;br /&gt;
&lt;br /&gt;
==Radial distribution function==&lt;br /&gt;
The following plot is of a typical [[radial distribution function]] for the monatomic Lennard-Jones liquid&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.1700653 John G. Kirkwood, Victor A. Lewinson, and Berni J. Alder &amp;quot;Radial Distribution Functions and the Equation of State of Fluids Composed of Molecules Interacting According to the Lennard-Jones Potential&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;20&#039;&#039;&#039; pp. 929- (1952)]&amp;lt;/ref&amp;gt; (here with &amp;lt;math&amp;gt;\sigma=3.73&amp;lt;/math&amp;gt;&amp;amp;Aring;  and &amp;lt;math&amp;gt;\epsilon=0.294&amp;lt;/math&amp;gt; kcal/mol at a [[temperature]] of 111.06K):&lt;br /&gt;
[[Image:LJ_rdf.png|center|450px|Typical radial distribution function for the monatomic Lennard-Jones liquid.]]&lt;br /&gt;
&lt;br /&gt;
==Helmholtz energy function==&lt;br /&gt;
An expression for the [[Helmholtz energy function]] of the [[Building up a face centered cubic lattice | face centred cubic]] solid has been given by van der Hoef &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.1314342 Martin A. van der Hoef &amp;quot;Free energy of the Lennard-Jones solid&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;113&#039;&#039;&#039; pp. 8142-8148 (2000)]&amp;lt;/ref&amp;gt;, applicable within the density range &amp;lt;math&amp;gt;0.94 \le \rho^* \le 1.20&amp;lt;/math&amp;gt; and the temperature range &amp;lt;math&amp;gt;0.1 \le T^* \le 2.0&amp;lt;/math&amp;gt;. For the liquid state see the work of Johnson, Zollweg and Gubbins &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1080/00268979300100411 J. Karl Johnson, John A. Zollweg and Keith E. Gubbins &amp;quot;The Lennard-Jones equation of state revisited&amp;quot;, Molecular Physics &#039;&#039;&#039;78&#039;&#039;&#039; pp. 591-618 (1993)]&amp;lt;/ref&amp;gt;.&lt;br /&gt;
&lt;br /&gt;
==Equation of state==&lt;br /&gt;
:&#039;&#039;Main article: [[Lennard-Jones equation of state]]&#039;&#039;&lt;br /&gt;
&lt;br /&gt;
==Virial coefficients==&lt;br /&gt;
:&#039;&#039;Main article: [[Lennard-Jones model: virial coefficients]]&#039;&#039;&lt;br /&gt;
&lt;br /&gt;
==Phase diagram==&lt;br /&gt;
:&#039;&#039;Main article: [[Phase diagram of the Lennard-Jones model]]&#039;&#039;&lt;br /&gt;
&lt;br /&gt;
==Zeno line==&lt;br /&gt;
It has been shown that the Lennard-Jones model has a straight [[Zeno line]] &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1021/jp802999z E. M. Apfelbaum, V. S. Vorob’ev and G. A. Martynov &amp;quot;Regarding the Theory of the Zeno Line&amp;quot;, Journal of Physical Chemistry A &#039;&#039;&#039;112&#039;&#039;&#039; pp. 6042-6044 (2008)]&amp;lt;/ref&amp;gt; on the [[Phase diagrams: Density-temperature plane |density-temperature plane]].&lt;br /&gt;
&lt;br /&gt;
==Widom line==&lt;br /&gt;
It has been shown that the Lennard-Jones model has a  [[Widom line]] &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1021/jp2039898 V. V. Brazhkin, Yu. D. Fomin, A. G. Lyapin, V. N. Ryzhov, and E. N. Tsiok &amp;quot;Widom Line for the Liquid–Gas Transition in Lennard-Jones System&amp;quot;, Journal of Physical Chemistry B Article ASAP (2011)]&amp;lt;/ref&amp;gt; on the [[Phase diagrams: Pressure-temperature plane | pressure-temperature plane]].&lt;br /&gt;
&lt;br /&gt;
==Perturbation theory==&lt;br /&gt;
The Lennard-Jones model is also used in [[Perturbation theory |perturbation theories]], for example see: [[Weeks-Chandler-Andersen perturbation theory]].&lt;br /&gt;
== Approximations in simulation: truncation and shifting ==&lt;br /&gt;
The Lennard-Jones model is often used with a cutoff radius of &amp;lt;math&amp;gt;2.5 \sigma&amp;lt;/math&amp;gt;, beyond which &amp;lt;math&amp;gt; \Phi_{12}(r)&amp;lt;/math&amp;gt; is set to zero. Setting the well depth &amp;lt;math&amp;gt; \epsilon &amp;lt;/math&amp;gt; to be 1 in the potential on arrives at &amp;lt;math&amp;gt; \Phi_{12}(r)\simeq  -0.0163&amp;lt;/math&amp;gt;, i.e. at this distance the potential is at less than 2% of the well depth. For an analysis of the effect of this cutoff on the melting line see the work of Mastny and  de Pablo  &amp;lt;ref name=&amp;quot;Mastny&amp;quot;&amp;gt; &amp;lt;/ref&amp;gt; and of Ahmed and Sadus &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.3481102  Alauddin Ahmed  and Richard J. Sadus &amp;quot;Effect of potential truncations and shifts on the solid-liquid phase coexistence of Lennard-Jones fluids&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;133&#039;&#039;&#039; 124515 (2010)]&amp;lt;/ref&amp;gt;. See Panagiotopoulos for critical parameters &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1007/BF01458815 A. Z. Panagiotopoulos &amp;quot;Molecular simulation of phase coexistence: Finite-size effects and determination of critical parameters for two- and three-dimensional Lennard-Jones fluids&amp;quot;, International Journal of Thermophysics &#039;&#039;&#039;15&#039;&#039;&#039; pp. 1057-1072 (1994)]&amp;lt;/ref&amp;gt;. It has recently been suggested that a truncated and shifted force cutoff of &amp;lt;math&amp;gt;1.5 \sigma&amp;lt;/math&amp;gt; can be used under certain conditions &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.3558787 Søren Toxvaerd and Jeppe C. Dyre &amp;quot;Communication: Shifted forces in molecular dynamics&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;134&#039;&#039;&#039; 081102 (2011)]&amp;lt;/ref&amp;gt;. In order to avoid any discontinuity, a piecewise continuous version, known as the  [[modified Lennard-Jones model]], was developed.&lt;br /&gt;
&lt;br /&gt;
== n-m García-Verdugo potential ==&lt;br /&gt;
It is relatively common to encounter potential functions given by:&lt;br /&gt;
: &amp;lt;math&amp;gt; \Phi_{12}(r) = c_{n,m} \epsilon   \left[ \left( \frac{ \sigma }{r } \right)^n - \left( \frac{\sigma}{r} \right)^m &lt;br /&gt;
\right].&lt;br /&gt;
&amp;lt;/math&amp;gt;&lt;br /&gt;
with &amp;lt;math&amp;gt; n &amp;lt;/math&amp;gt; and &amp;lt;math&amp;gt; m &amp;lt;/math&amp;gt; being positive integers and &amp;lt;math&amp;gt; n &amp;gt; m &amp;lt;/math&amp;gt;.&lt;br /&gt;
&amp;lt;math&amp;gt; c_{n,m} &amp;lt;/math&amp;gt;  is chosen such that the minimum value of &amp;lt;math&amp;gt; \Phi_{12}(r) &amp;lt;/math&amp;gt; being &amp;lt;math&amp;gt; \Phi_{min} = - \epsilon &amp;lt;/math&amp;gt;.&lt;br /&gt;
Such forms are usually referred to as &#039;&#039;&#039;n-m Lennard-Jones Potential&#039;&#039;&#039;.&lt;br /&gt;
For example, the [[9-3 Lennard-Jones potential |9-3 Lennard-Jones interaction potential]] is often used to model the interaction between&lt;br /&gt;
a continuous solid wall and the atoms/molecules of a liquid.&lt;br /&gt;
On the &#039;9-3 Lennard-Jones potential&#039; page  a justification of this use is presented. Another example is the [[n-6 Lennard-Jones potential]],&lt;br /&gt;
where &amp;lt;math&amp;gt;m&amp;lt;/math&amp;gt; is fixed at 6, and &amp;lt;math&amp;gt;n&amp;lt;/math&amp;gt; is free to adopt a range of integer values.&lt;br /&gt;
The potentials form part of the larger class of potentials known as the [[Mie potential]].&lt;br /&gt;
&amp;lt;br&amp;gt;&lt;br /&gt;
Examples:&lt;br /&gt;
*[[8-6 Lennard-Jones potential]]&lt;br /&gt;
*[[9-3 Lennard-Jones potential]]&lt;br /&gt;
*[[9-6 Lennard-Jones potential]]&lt;br /&gt;
*[[10-4-3 Lennard-Jones potential]]&lt;br /&gt;
*[[200-100 Lennard-Jones potential]]&lt;br /&gt;
*[[n-6 Lennard-Jones potential]]&lt;br /&gt;
&lt;br /&gt;
==Mixtures==&lt;br /&gt;
*[[Binary Lennard-Jones mixtures]]&lt;br /&gt;
*[[Multicomponent Lennard-Jones mixtures]]&lt;br /&gt;
&lt;br /&gt;
==Related models==&lt;br /&gt;
*[[Kihara potential]]&lt;br /&gt;
*[[Lennard-Jones model in 1-dimension]] (rods)&lt;br /&gt;
*[[Lennard-Jones disks | Lennard-Jones model in 2-dimensions]] (disks)&lt;br /&gt;
*[[Lennard-Jones model in 4-dimensions]] &lt;br /&gt;
*[[Lennard-Jones sticks]]&lt;br /&gt;
*[[Mie potential]]&lt;br /&gt;
*[[Soft-core Lennard-Jones model]]&lt;br /&gt;
*[[Soft sphere potential]]&lt;br /&gt;
*[[Stockmayer potential]]&lt;br /&gt;
&lt;br /&gt;
==References==&lt;br /&gt;
&amp;lt;references /&amp;gt;&lt;br /&gt;
[[Category:Models]]&lt;/div&gt;</summary>
		<author><name>146.155.46.185</name></author>
	</entry>
	<entry>
		<id>http://www.sklogwiki.org/SklogWiki/index.php?title=Lennard-Jones_model&amp;diff=14117</id>
		<title>Lennard-Jones model</title>
		<link rel="alternate" type="text/html" href="http://www.sklogwiki.org/SklogWiki/index.php?title=Lennard-Jones_model&amp;diff=14117"/>
		<updated>2014-04-01T19:42:39Z</updated>

		<summary type="html">&lt;p&gt;146.155.46.185: /* n-m Lennard-Jones potential */&lt;/p&gt;
&lt;hr /&gt;
&lt;div&gt;The &#039;&#039;&#039;Lennard-Jones&#039;&#039;&#039; [[intermolecular pair potential]] is a special case of the [[Mie potential]] and takes its name from  [[ Sir John Edward Lennard-Jones KBE, FRS | Sir John Edward Lennard-Jones]] &lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1098/rspa.1924.0081  John Edward Lennard-Jones &amp;quot;On the Determination of Molecular Fields. I. From the Variation of the Viscosity of a Gas with Temperature&amp;quot;, 	Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character &#039;&#039;&#039;106&#039;&#039;&#039; pp. 	441-462 (1924)] &amp;amp;sect; 8 (ii)&amp;lt;/ref&amp;gt; &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1098/rspa.1924.0082 John Edward Lennard-Jones &amp;quot;On the Determination of Molecular Fields. II. From the Equation of State of a Gas&amp;quot;,  Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character &#039;&#039;&#039;106&#039;&#039;&#039; pp. 463-477 (1924)] Eq. 2.05&amp;lt;/ref&amp;gt;.&lt;br /&gt;
The Lennard-Jones [[models |model]] consists of two &#039;parts&#039;; a steep repulsive term, and&lt;br /&gt;
smoother attractive term, representing the London dispersion forces &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1007/BF01421741 F. London &amp;quot;Zur Theorie und Systematik der Molekularkräfte&amp;quot;, Zeitschrift für Physik A Hadrons and Nuclei &#039;&#039;&#039;63&#039;&#039;&#039; pp. 245-279 (1930)]&amp;lt;/ref&amp;gt;. Apart from being an important model in itself,&lt;br /&gt;
the Lennard-Jones potential frequently forms one of &#039;building blocks&#039; of many [[force fields]]. It is worth mentioning that the 12-6 Lennard-Jones model is not the &lt;br /&gt;
most faithful representation of the potential energy surface, but rather its use is widespread due to its computational expediency.&lt;br /&gt;
For example, the repulsive term is maybe better described with the [[exp-6 potential]].&lt;br /&gt;
One of the first [[Computer simulation techniques |computer simulations]] using the Lennard-Jones model was undertaken by Wood and Parker in 1957 &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.1743822 W. W. Wood and F. R. Parker &amp;quot;Monte Carlo Equation of State of Molecules Interacting with the Lennard‐Jones Potential. I. A Supercritical Isotherm at about Twice the Critical Temperature&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;27&#039;&#039;&#039; pp. 720- (1957)]&amp;lt;/ref&amp;gt; in a  study of liquid [[argon]].&lt;br /&gt;
&lt;br /&gt;
== Functional form == &lt;br /&gt;
The Lennard-Jones potential is given by&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt; \Phi_{12}(r) = 4 \epsilon \left[ \left(\frac{\sigma}{r} \right)^{12}-  \left( \frac{\sigma}{r}\right)^6 \right] &amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
or is sometimes expressed as &lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt; \Phi_{12}(r) = \frac{A}{r^{12}}-  \frac{B}{r^6}&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
where&lt;br /&gt;
* &amp;lt;math&amp;gt;r := |\mathbf{r}_1 - \mathbf{r}_2|&amp;lt;/math&amp;gt;&lt;br /&gt;
* &amp;lt;math&amp;gt; \Phi_{12}(r) &amp;lt;/math&amp;gt; is the [[intermolecular pair potential]] between two particles or &#039;&#039;sites&#039;&#039;&lt;br /&gt;
* &amp;lt;math&amp;gt; \sigma &amp;lt;/math&amp;gt; is the value of &amp;lt;math&amp;gt;r&amp;lt;/math&amp;gt; at which &amp;lt;math&amp;gt; \Phi_{12}(r)=0&amp;lt;/math&amp;gt;&lt;br /&gt;
* &amp;lt;math&amp;gt; \epsilon &amp;lt;/math&amp;gt; is the well depth (energy)&lt;br /&gt;
* &amp;lt;math&amp;gt;A= 4\epsilon \sigma^{12}&amp;lt;/math&amp;gt;, &amp;lt;math&amp;gt;B= 4\epsilon \sigma^{6}&amp;lt;/math&amp;gt;&lt;br /&gt;
* Minimum value of &amp;lt;math&amp;gt; \Phi_{12}(r) &amp;lt;/math&amp;gt; at &amp;lt;math&amp;gt; r = r_{min} &amp;lt;/math&amp;gt;;  &lt;br /&gt;
: &amp;lt;math&amp;gt; \frac{r_{min}}{\sigma} = 2^{1/6} \simeq   1.12246 ...  &amp;lt;/math&amp;gt;&lt;br /&gt;
In reduced units: &lt;br /&gt;
* Density: &amp;lt;math&amp;gt; \rho^* := \rho \sigma^3 &amp;lt;/math&amp;gt;&lt;br /&gt;
where &amp;lt;math&amp;gt; \rho := N/V &amp;lt;/math&amp;gt; (number of particles &amp;lt;math&amp;gt; N &amp;lt;/math&amp;gt; divided by the volume &amp;lt;math&amp;gt; V &amp;lt;/math&amp;gt;)&lt;br /&gt;
* Temperature: &amp;lt;math&amp;gt; T^* := k_B T/\epsilon &amp;lt;/math&amp;gt;&lt;br /&gt;
where &amp;lt;math&amp;gt; T &amp;lt;/math&amp;gt;  is the absolute [[temperature]] and &amp;lt;math&amp;gt; k_B &amp;lt;/math&amp;gt; is the [[Boltzmann constant]]&lt;br /&gt;
&lt;br /&gt;
The following is a plot of the Lennard-Jones model for the Rowley, Nicholson and Parsonage parameter set &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1016/0021-9991(75)90042-X   L. A. Rowley, D. Nicholson and N. G. Parsonage &amp;quot;Monte Carlo grand canonical ensemble calculation in a gas-liquid transition region for 12-6 Argon&amp;quot;, Journal of Computational Physics  &#039;&#039;&#039;17&#039;&#039;&#039; pp. 401-414 (1975)]&amp;lt;/ref&amp;gt; (&amp;lt;math&amp;gt;\epsilon/k_B = &amp;lt;/math&amp;gt; 119.8 K and &amp;lt;math&amp;gt;\sigma=&amp;lt;/math&amp;gt; 0.3405 nm). See [[argon]] for other parameter sets.&amp;lt;br&amp;gt;&lt;br /&gt;
[[Image:Lennard-Jones.png|500px]]&lt;br /&gt;
==Critical point==&lt;br /&gt;
The location of the [[Critical points |critical point]] is &lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.477099  J. M. Caillol &amp;quot; Critical-point of the Lennard-Jones fluid: A finite-size scaling study&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;109&#039;&#039;&#039; pp. 4885-4893 (1998)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
:&amp;lt;math&amp;gt;T_c^* = 1.326 \pm 0.002&amp;lt;/math&amp;gt;&lt;br /&gt;
at a reduced density of&lt;br /&gt;
:&amp;lt;math&amp;gt;\rho_c^* = 0.316 \pm 0.002&amp;lt;/math&amp;gt;&lt;br /&gt;
The critical [[compressibility factor]] is given by &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.4829837 V. L. Kulinskii &amp;quot;The critical compressibility factor of fluids from the global isomorphism approach&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;139&#039;&#039;&#039; 184119 (2013)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;Z_c = \frac{p_cv_c}{RT_c} = 0.281&amp;lt;/math&amp;gt; &lt;br /&gt;
&lt;br /&gt;
Vliegenthart and Lekkerkerker&lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.481106 G. A. Vliegenthart and H. N. W. Lekkerkerker &amp;quot;Predicting the gas–liquid critical point from the second virial coefficient&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;112&#039;&#039;&#039; pp. 5364-5369 (2000)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.3496468  L. A. Bulavin  and V. L. Kulinskii &amp;quot;Generalized principle of corresponding states and the scale invariant mean-field approach&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;&#039;133&#039;&#039;&#039; 134101 (2010)]&amp;lt;/ref&amp;gt;&lt;br /&gt;
have suggested that the critical point is related to the [[second virial coefficient]] via the expression &lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;B_2 \vert_{T=T_c}= -\pi \sigma^3&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
==Triple point==&lt;br /&gt;
The location of the [[triple point]] as found by Mastny and  de Pablo &amp;lt;ref name=&amp;quot;Mastny&amp;quot;&amp;gt; [http://dx.doi.org/10.1063/1.2753149     Ethan A. Mastny and Juan J. de Pablo &amp;quot;Melting line of the Lennard-Jones system, infinite size, and full potential&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;127&#039;&#039;&#039; 104504 (2007)]&amp;lt;/ref&amp;gt; is&lt;br /&gt;
:&amp;lt;math&amp;gt;T_{tp}^* = 0.694&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;\rho_{tp}^* = 0.84&amp;lt;/math&amp;gt; (liquid); &lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;\rho_{tp}^* = 0.96&amp;lt;/math&amp;gt; (solid).&lt;br /&gt;
&lt;br /&gt;
==Radial distribution function==&lt;br /&gt;
The following plot is of a typical [[radial distribution function]] for the monatomic Lennard-Jones liquid&amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.1700653 John G. Kirkwood, Victor A. Lewinson, and Berni J. Alder &amp;quot;Radial Distribution Functions and the Equation of State of Fluids Composed of Molecules Interacting According to the Lennard-Jones Potential&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;20&#039;&#039;&#039; pp. 929- (1952)]&amp;lt;/ref&amp;gt; (here with &amp;lt;math&amp;gt;\sigma=3.73&amp;lt;/math&amp;gt;&amp;amp;Aring;  and &amp;lt;math&amp;gt;\epsilon=0.294&amp;lt;/math&amp;gt; kcal/mol at a [[temperature]] of 111.06K):&lt;br /&gt;
[[Image:LJ_rdf.png|center|450px|Typical radial distribution function for the monatomic Lennard-Jones liquid.]]&lt;br /&gt;
&lt;br /&gt;
==Helmholtz energy function==&lt;br /&gt;
An expression for the [[Helmholtz energy function]] of the [[Building up a face centered cubic lattice | face centred cubic]] solid has been given by van der Hoef &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.1314342 Martin A. van der Hoef &amp;quot;Free energy of the Lennard-Jones solid&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;113&#039;&#039;&#039; pp. 8142-8148 (2000)]&amp;lt;/ref&amp;gt;, applicable within the density range &amp;lt;math&amp;gt;0.94 \le \rho^* \le 1.20&amp;lt;/math&amp;gt; and the temperature range &amp;lt;math&amp;gt;0.1 \le T^* \le 2.0&amp;lt;/math&amp;gt;. For the liquid state see the work of Johnson, Zollweg and Gubbins &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1080/00268979300100411 J. Karl Johnson, John A. Zollweg and Keith E. Gubbins &amp;quot;The Lennard-Jones equation of state revisited&amp;quot;, Molecular Physics &#039;&#039;&#039;78&#039;&#039;&#039; pp. 591-618 (1993)]&amp;lt;/ref&amp;gt;.&lt;br /&gt;
&lt;br /&gt;
==Equation of state==&lt;br /&gt;
:&#039;&#039;Main article: [[Lennard-Jones equation of state]]&#039;&#039;&lt;br /&gt;
&lt;br /&gt;
==Virial coefficients==&lt;br /&gt;
:&#039;&#039;Main article: [[Lennard-Jones model: virial coefficients]]&#039;&#039;&lt;br /&gt;
&lt;br /&gt;
==Phase diagram==&lt;br /&gt;
:&#039;&#039;Main article: [[Phase diagram of the Lennard-Jones model]]&#039;&#039;&lt;br /&gt;
&lt;br /&gt;
==Zeno line==&lt;br /&gt;
It has been shown that the Lennard-Jones model has a straight [[Zeno line]] &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1021/jp802999z E. M. Apfelbaum, V. S. Vorob’ev and G. A. Martynov &amp;quot;Regarding the Theory of the Zeno Line&amp;quot;, Journal of Physical Chemistry A &#039;&#039;&#039;112&#039;&#039;&#039; pp. 6042-6044 (2008)]&amp;lt;/ref&amp;gt; on the [[Phase diagrams: Density-temperature plane |density-temperature plane]].&lt;br /&gt;
&lt;br /&gt;
==Widom line==&lt;br /&gt;
It has been shown that the Lennard-Jones model has a  [[Widom line]] &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1021/jp2039898 V. V. Brazhkin, Yu. D. Fomin, A. G. Lyapin, V. N. Ryzhov, and E. N. Tsiok &amp;quot;Widom Line for the Liquid–Gas Transition in Lennard-Jones System&amp;quot;, Journal of Physical Chemistry B Article ASAP (2011)]&amp;lt;/ref&amp;gt; on the [[Phase diagrams: Pressure-temperature plane | pressure-temperature plane]].&lt;br /&gt;
&lt;br /&gt;
==Perturbation theory==&lt;br /&gt;
The Lennard-Jones model is also used in [[Perturbation theory |perturbation theories]], for example see: [[Weeks-Chandler-Andersen perturbation theory]].&lt;br /&gt;
== Approximations in simulation: truncation and shifting ==&lt;br /&gt;
The Lennard-Jones model is often used with a cutoff radius of &amp;lt;math&amp;gt;2.5 \sigma&amp;lt;/math&amp;gt;, beyond which &amp;lt;math&amp;gt; \Phi_{12}(r)&amp;lt;/math&amp;gt; is set to zero. Setting the well depth &amp;lt;math&amp;gt; \epsilon &amp;lt;/math&amp;gt; to be 1 in the potential on arrives at &amp;lt;math&amp;gt; \Phi_{12}(r)\simeq  -0.0163&amp;lt;/math&amp;gt;, i.e. at this distance the potential is at less than 2% of the well depth. For an analysis of the effect of this cutoff on the melting line see the work of Mastny and  de Pablo  &amp;lt;ref name=&amp;quot;Mastny&amp;quot;&amp;gt; &amp;lt;/ref&amp;gt; and of Ahmed and Sadus &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.3481102  Alauddin Ahmed  and Richard J. Sadus &amp;quot;Effect of potential truncations and shifts on the solid-liquid phase coexistence of Lennard-Jones fluids&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;133&#039;&#039;&#039; 124515 (2010)]&amp;lt;/ref&amp;gt;. See Panagiotopoulos for critical parameters &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1007/BF01458815 A. Z. Panagiotopoulos &amp;quot;Molecular simulation of phase coexistence: Finite-size effects and determination of critical parameters for two- and three-dimensional Lennard-Jones fluids&amp;quot;, International Journal of Thermophysics &#039;&#039;&#039;15&#039;&#039;&#039; pp. 1057-1072 (1994)]&amp;lt;/ref&amp;gt;. It has recently been suggested that a truncated and shifted force cutoff of &amp;lt;math&amp;gt;1.5 \sigma&amp;lt;/math&amp;gt; can be used under certain conditions &amp;lt;ref&amp;gt;[http://dx.doi.org/10.1063/1.3558787 Søren Toxvaerd and Jeppe C. Dyre &amp;quot;Communication: Shifted forces in molecular dynamics&amp;quot;, Journal of Chemical Physics &#039;&#039;&#039;134&#039;&#039;&#039; 081102 (2011)]&amp;lt;/ref&amp;gt;. In order to avoid any discontinuity, a piecewise continuous version, known as the  [[modified Lennard-Jones model]], was developed.&lt;br /&gt;
&lt;br /&gt;
== n-m García Verdugo potential ==&lt;br /&gt;
It is relatively common to encounter potential functions given by:&lt;br /&gt;
: &amp;lt;math&amp;gt; \Phi_{12}(r) = c_{n,m} \epsilon   \left[ \left( \frac{ \sigma }{r } \right)^n - \left( \frac{\sigma}{r} \right)^m &lt;br /&gt;
\right].&lt;br /&gt;
&amp;lt;/math&amp;gt;&lt;br /&gt;
with &amp;lt;math&amp;gt; n &amp;lt;/math&amp;gt; and &amp;lt;math&amp;gt; m &amp;lt;/math&amp;gt; being positive integers and &amp;lt;math&amp;gt; n &amp;gt; m &amp;lt;/math&amp;gt;.&lt;br /&gt;
&amp;lt;math&amp;gt; c_{n,m} &amp;lt;/math&amp;gt;  is chosen such that the minimum value of &amp;lt;math&amp;gt; \Phi_{12}(r) &amp;lt;/math&amp;gt; being &amp;lt;math&amp;gt; \Phi_{min} = - \epsilon &amp;lt;/math&amp;gt;.&lt;br /&gt;
Such forms are usually referred to as &#039;&#039;&#039;n-m Lennard-Jones Potential&#039;&#039;&#039;.&lt;br /&gt;
For example, the [[9-3 Lennard-Jones potential |9-3 Lennard-Jones interaction potential]] is often used to model the interaction between&lt;br /&gt;
a continuous solid wall and the atoms/molecules of a liquid.&lt;br /&gt;
On the &#039;9-3 Lennard-Jones potential&#039; page  a justification of this use is presented. Another example is the [[n-6 Lennard-Jones potential]],&lt;br /&gt;
where &amp;lt;math&amp;gt;m&amp;lt;/math&amp;gt; is fixed at 6, and &amp;lt;math&amp;gt;n&amp;lt;/math&amp;gt; is free to adopt a range of integer values.&lt;br /&gt;
The potentials form part of the larger class of potentials known as the [[Mie potential]].&lt;br /&gt;
&amp;lt;br&amp;gt;&lt;br /&gt;
Examples:&lt;br /&gt;
*[[8-6 Lennard-Jones potential]]&lt;br /&gt;
*[[9-3 Lennard-Jones potential]]&lt;br /&gt;
*[[9-6 Lennard-Jones potential]]&lt;br /&gt;
*[[10-4-3 Lennard-Jones potential]]&lt;br /&gt;
*[[200-100 Lennard-Jones potential]]&lt;br /&gt;
*[[n-6 Lennard-Jones potential]]&lt;br /&gt;
&lt;br /&gt;
==Mixtures==&lt;br /&gt;
*[[Binary Lennard-Jones mixtures]]&lt;br /&gt;
*[[Multicomponent Lennard-Jones mixtures]]&lt;br /&gt;
&lt;br /&gt;
==Related models==&lt;br /&gt;
*[[Kihara potential]]&lt;br /&gt;
*[[Lennard-Jones model in 1-dimension]] (rods)&lt;br /&gt;
*[[Lennard-Jones disks | Lennard-Jones model in 2-dimensions]] (disks)&lt;br /&gt;
*[[Lennard-Jones model in 4-dimensions]] &lt;br /&gt;
*[[Lennard-Jones sticks]]&lt;br /&gt;
*[[Mie potential]]&lt;br /&gt;
*[[Soft-core Lennard-Jones model]]&lt;br /&gt;
*[[Soft sphere potential]]&lt;br /&gt;
*[[Stockmayer potential]]&lt;br /&gt;
&lt;br /&gt;
==References==&lt;br /&gt;
&amp;lt;references /&amp;gt;&lt;br /&gt;
[[Category:Models]]&lt;/div&gt;</summary>
		<author><name>146.155.46.185</name></author>
	</entry>
</feed>