Talk:Lennard-Jones potential

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Chemistry Mid‑importance

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Archives

Archive 1 2005-present

Does Buckingham potential belong?[edit]

Should the equation for Buckingham potential be presented? Should it even be mentioned except for a link in the see also? I believe that this should be cut because it doesn't really add anything about the LJ pontential and I don't see how something presented earlier(LJ) could approximate something presented later(Buckingham). If anything the Buckingham refined the LJ but since it is not very common that is questionable as well.

Phancy Physicist (talk) 18:50, 29 December 2010 (UTC)[reply]

It was added Dec.1 and incorrectly attributed to LJ himself, which would be a reason to include it if true. On Dec.25 I changed the attribution to Buckingham, but did not really think about removing it. The reference cited (Atkins) does say that "there is plenty of evidence to show that 1/r¹² is a very poor representation of the repulsive potential, and that an exponential form is greatly superior". However admittedly Atkins is only a physical chemistry text and those of you (not me) who use such potentials are probably more up-to-date with the evidence.

I suggest that both the Buckingham and Morse potentials be placed in a brief last section called, perhaps called Refinements of the L-J potential. We could say (with dates) that LJ was the first attempt at a potential function between two neutral atoms, and mention Buckingham and Morse as the first two attempts at refinement, and perhaps a few more recent versions too. This would give a little more context then just a See also section. Dirac66 (talk) 19:33, 29 December 2010 (UTC)[reply]

I like the idea of a refinements section. We just have to be careful of what potentials we call refinements of LJ in order to not take due credit from others. I have to check Morse's paper but he proposed his potential in 1929 so it could have been independently developed by him as easily as it could have been inspired by Lennard-Jones.

Phancy Physicist (talk) 19:54, 29 December 2010 (UTC)[reply]

Example values for Lennard_Jones Potential[edit]

After working on this forever, I could never find the proper values to match a theoretical atom that would properly work within this formula.

Argon Values: sigma, σ 3.405 epsilon, ε 120 m 11

Source: http://inside.mines.edu/~dwu/classes/chen610/projects/Sp06/Barkley%20statmech2.pdf

I would like to suggest sharing this information on the wiki page. — Preceding unsigned comment added by 74.167.120.101 (talk) 21:35, 20 February 2012 (UTC)[reply]

I am a little confused: the 3.405, 120 values are very similar to those of Rowley, Nicholson and Parsonage (see Argon on SklogWiki) for the Lennard-Jones model. However, the m=11 corresponds to equation 6 in you project for the m-6-8 potential function and the parameters are very similar to those of Klein and Hanley (see Caligaris and Rodriguez) --Spud Gun (talk) 11:54, 21 February 2012 (UTC)[reply]

I would not be opposed to adding in example values but I would like to be very careful about how it is presented. Though there are numbers which people swear to for σ and ε, these number are highly situation dependent and even sometimes come down to what exactly you are trying to model. What I mostly worry about is whatever values we decide to show would become "The Values" for anyone who casually reads up on the LJ potential. Perhaps giving the impression of a kind of "universality" for the numbers shown.

Phancy Physicist (talk) 21:37, 21 February 2012 (UTC)[reply]

Rayleigh-Taylor instability[edit]

One of the figures in this article is a Rayleigh-Taylor instability. It is in the computational physics box, but it seems irrelevant to me for this article. Any suggestions here? — Preceding unsigned comment added by 145.94.187.200 (talk) 07:29, 21 August 2012 (UTC)[reply]

Move to "Lennard–Jones potential" (containing en-dash instead of hypen-minus)[edit]

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section.

The result of the move request was: request withdrawn. Favonian (talk) 21:22, 25 August 2012 (UTC)[reply]

Lennard-Jones potential → Lennard–Jones potential – "Lennard–Jones" contains an en-dash (see for example the article Navier–Stokes equations as a comparison), and not a hyphen-minus as is currently in the article title. I tried moving the article manually, but there's already a redirection page to this article with that name. —Kri (talk) 03:19, 24 August 2012 (UTC)[reply]

Oppose, this is correct here. The endash is only used if we combine the names of two people, e.g. Claude-Louis Navier and George Gabriel Stokes, but this is only named after one guy. --The Evil IP address (talk) 15:36, 24 August 2012 (UTC)[reply]

Aha, I thought Lennard and Jones were two different guys :P I guess this settles it then. Should the move request be removed now or doesn't it matter if we leave it here? —Kri (talk) 21:17, 25 August 2012 (UTC)[reply]

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

Inconsistency between the first plot and the LJ equation[edit]

According to the first equation and the x axis of the plot being in units of sigma, the minimum of potential in the figure should be r_m/sigma (not r_m) — Preceding unsigned comment added by 129.237.99.102 (talk) 02:05, 26 March 2014 (UTC)[reply]

Indexes should be upright[edit]

To write "LJ" as an index for a potential V ist to name the potential (and LJ is a mere name not a parameter), so one should have upright indexes. May someone please change this. Jjh1993 (talk) 14:43, 4 February 2015 (UTC)[reply]

I just changed all non-variable subscripts to upright, that includes abbreviations for truncated, cutoff, etc. --Jkokorian (talk) 09:58, 2 September 2016 (UTC)[reply]

Variables should be declared with units[edit]

When variables are first introduced, their units should be explicitly mentioned. To me, as an electrical engineer 'potential' implies that the unit is Volt, but I've even seen Lennard-Jones potential curves with a 'potential' in 1/cm. Could someone please add the correct units? I would do it myself, but I don't know what they are... --Jkokorian (talk) 10:04, 2 September 2016 (UTC)[reply]

Notation inconsistencies[edit]

σ and r_m are used in the LJ potential equations but later on in "Explanation", r_0 is used for the Buckingham potential without an explanation as to what it is. Is it σ, r_m or something else? r_0 is also used in "Alternative expressions", subsection "AB form" where is states that at r_0, V = − ε. This would mean, at least for this part, that r_0 = r_m and two different notations are used. — Preceding unsigned comment added by Jvillatoro leal (talk • contribs) 09:58, 19 January 2018 (UTC)[reply]