Talk:Lennard-Jones potential

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Help with this template Comments: edit – history – watch – refresh In the article it says: "σ is the (finite) distance at which the interparticle force is zero." This is not quite true. Like someone else mentioned, σ is the distance at which the potential is zero. The interparticle force will be zero when the first derivative of the potential (i.e. the force, up to a sign) is zero. That happens at . Jasonrunguitar 16:49, 12 July 2007 (UTC)

Doesn't the Lennard-Jones potential describe the potential energy between two atoms at a distance r and not just the strength of the two forces when they balance as stated by the first paragraph? Zapateria 17:52, May 25, 2005 (UTC)

Good point. The article assumes the reader knows that the force is given by . Perhaps it should state it?

I would be interested in seeing analytical solutions for properties of the Lennard-Jones potential, assuming that there are any. I've not been very successful in finding any myself or in the literature. 66.21.139.18 12:42, 27 March 2006 (UTC)Gabriel Hanna

Probably the most interesting analytical property is the position of the minimum, which can be obtained using differential calculus (I think it was something like sigma*2^(1/12) but I'm too lazy to check right now...). Itub 23:53, 8 April 2006 (UTC)

The minima of the potential is at 2^1/6 sigma. The first zero point is at sigma. I'm not sure what exactly you mean by analytical solutions for the properties since it's unclear what properties you are talking about. Simpleliquid 17:40, 18 December 2006 (UTC)

Or if you are thinking about rare gases have a look here: http://link.aps.org/abstract/PRB/v73/e064112; doi: 10.1103/PhysRevB.73.064112.

Contents 1 Hard sphere diameter 2 Mistake in formula for FORCE 3 Definition of r 4 Parameter

[edit] Hard sphere diameter

I think that "hard sphere diameter" should be defined, or at least there should be a link to a page that defines it. Zeroparallax 21:23, 1 September 2006 (UTC)

Oh! And shouldn't it be the "hard sphere radius" rather than "diameter"? Zeroparallax 21:26, 1 September 2006 (UTC)

The hard sphere diameter is not a well defined quantity for a Lennard-Jones system. I removed the sentence that said that sigma was the hard-sphere radius because it was wrong. The Stokes-Einstein relationship with slip conditions, the viscosity, temperature and Diffusion constant of a LJ fluid can be used to obtain an effective hard-sphere diameter but I think this is beyond the scope of this stub. Simpleliquid 17:30, 18 December 2006 (UTC)

Aren't van der Waals forces occasionally repulsive? The opening paragraph suggests they are always attractive.128.243.220.21 11:46, 21 March 2007 (UTC)

[edit] Mistake in formula for FORCE

F = -dV/dr = 4*epsilon*( .. ) and not 8*epsilon*( .. ) as displayed!

[edit] Definition of r

I readded a line explaining what r is in the equations as it was not defined anywhere in the article after the previous edit. Zapateria (talk) 22:13, 18 February 2008 (UTC)

[edit] Parameter

What are the numerical parameters used in the plot?