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Re: [ESPResSo] question about espresso( program is attached)

From: Owen Hickey
Subject: Re: [ESPResSo] question about espresso( program is attached)
Date: Thu, 14 Feb 2008 15:03:17 -0500


I think the actual result for the pressure is P=1/D^3 (note I am using = instead of scales like).  The discrepancy is because you assumed the length of tube in which the polymer is contained is independent of D and you took the derivative of the free energy with respect to D instead of the volume ( V=D^(4/3) )...  Of course this is still not the result you get and I think the first thing I might try would be to make the radius of gyration of the polymer much bigger than the tube diameter (they are about the same currently if I am not mistaken).  The other potential reason I can see for a discrepancy would be that you have an implicit fluid.  You might also want to try adding some un-bonded lennard-jones beads to represent fluid (a density of about 0.8 should make a reasonable fluid and using a DPD thermostat instead of langevin.  Not sure if either of those will work...

Hope that helps,
Owen Hickey

2008/2/13 R. Abbasi <address@hidden>:

Hello Dear,

      I study physics (MSC. Condensed matter) and my project  is about polymer.

I 'm going to do with' espresso'.

     Before do this, I have written a program to calculate osmotic pressure or free energy of confinement of a polymer chain without any charge into a cylindrical pore of diameter D.

According Flory  theorem those must be a power low  with D.

                         osmotic pressure  α  ( diameter of cylinder) ^ (-8/3)
                 free energy of confinement  α ( diameter of cylinder) ^ (-5/3)

     But my program's result is not acceptable at all. So may I ask you to help me about that?

I have attached my program and result also.

Thank you very much

Sincerely yours,


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