Load up some frames into VMD and start measuring the distances shown by the 
peaks in your RDF, link them with what you actually see in there (using 
something like a transparent representation of the carbon atom(s) using VDW 
then set the sphere scale so that it matches the correct radius, may be an 
easier way to do this, but this would make it easy to see).  Appears it may be 
something real, so just check the coordinate file and see where they are 
actually coming from.

Catch ya,

Dr. Dallas Warren
Medicinal Chemistry and Drug Action
Monash Institute of Pharmaceutical Sciences, Monash University
381 Royal Parade, Parkville VIC 3010
dallas.war...@monash.edu
+61 3 9903 9304
---------------------------------
When the only tool you own is a hammer, every problem begins to resemble a nail.

From: gmx-users-boun...@gromacs.org [mailto:gmx-users-boun...@gromacs.org] On 
Behalf Of Moeed
Sent: Friday, 16 September 2011 12:55 AM
To: jalem...@vt.edu; Discussion list for GROMACS users
Subject: Re: [gmx-users] radial distribution function

Hello again,

I tried comparing RDF plots generated by sampling from 4 to 5 ns run and a 
longer run from 4 to 30 ns to see whether the small jumps on the plot are due 
to insufficient sampling. Attached is the new plot showing that two RDF curves 
are almost identical. I only wanted to let you know and please comment on the 
attached plot if you have any ideas. Thank you. :)

Moeed
On Sat, Sep 10, 2011 at 10:00 AM, Moeed 
<lecie...@googlemail.com<mailto:lecie...@googlemail.com>> wrote:
Thank you for your input. I am going to run for another 15 ns to see if the 
little jumps vanish.

Best,

On Fri, Sep 9, 2011 at 9:16 PM, Justin A. Lemkul 
<jalem...@vt.edu<mailto:jalem...@vt.edu>> wrote:


lina wrote:



On Sat, Sep 10, 2011 at 3:35 AM, Moeed 
<lecie...@googlemail.com<mailto:lecie...@googlemail.com> 
<mailto:lecie...@googlemail.com<mailto:lecie...@googlemail.com>>> wrote:

   Dear users,

   I have created radial distribution function plot for Carbon atoms in
   a system containing polymer chains. I see some little jumps between
   first and second peak.
   I need your help to comment on how this behavior can be justified
   (or if the plot is wrong).

   g_rdf -f *.trr -s *.tpr -o *.xvg -n *.ndx -b xxx
   Thank you in advance.


I think your figure is fine.

I think, based on information given in subsequent messages, that there is 
insufficient data collection to assess whether this RDF plot is as meaningful 
as it could be.  There is nothing glaringly wrong, but the roughness is due to 
insufficient sampling.


You just need how to proper interpret your figures, truly understand what the 
"radial distribution" means.


I think it inappropriate to suggest that the OP does not understand the concept 
behind the figure; some guidance, perhaps is necessary, but nothing more.


-Justin

--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu<http://vt.edu> | (540) 231-9080<tel:%28540%29%20231-9080>
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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