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From: | Zunjing Wang |
Subject: | [ESPResSo] A bug in tab.h ---- Re: Surface Tension - simplebilayer.tcl |
Date: | Wed, 15 Jul 2009 11:46:46 -0400 |
User-agent: | Microsoft-Entourage/11.4.0.080122 |
Dear All,
I need to calculate the surface tension of a planar membrane.
I believe that the surface tension is calculated something like:
gamma = Lz*(Pzz-(Pxx+Pyy)/2).
So, if this equation is correct, I have to calculate the pressure tensor and
then using the components (average) Pzz,Pxx & Pyy to obtain gamma, right?
I was wondering though, is the pressure tensor and hence surface tension
calculated over the entire simulation box? Should I divide by two?
Besides, I have been working a little with mbtools package. I ran some simulations
for the simplebilayer script, but I get different results with the analytical and
tabulated potentials.
Here are some lines of the scripts:
====================================================================================================
set moltypes [list { 0 lipid { 0 1 1 } { 0 1 } } ]
===Tabulated
lappend nb_interactions [list 0 0 tabulated 9_095_11.tab ]
lappend nb_interactions [list 0 1 tabulated 9_095_11.tab ]
lappend nb_interactions [list 1 1 tabulated n9_c160_22.tab ]
===Defined Potential
set lj_eps 1.0
set lj_cutoff 2.5
set ljshift 0.0
set ljoffset 0.0
set lj_sigmah 0.95
set lj_sigma 1.0
lappend nb_interactions [list 0 0 lennard-jones $lj_eps $lj_sigmah [expr 1.1225*$lj_sigmah] [expr 0.25*$lj_eps] $ljoffset ]
lappend nb_interactions [list 0 1 lennard-jones $lj_eps $lj_sigmah [expr 1.1225*$lj_sigmah] [expr 0.25*$lj_eps] $ljoffset ]
lappend nb_interactions [list 1 1 lennard-jones $lj_eps $lj_sigma [expr 1.1225*$lj_sigma] [expr 0.25*$lj_eps] $ljoffset ]
# We use a special type of cosine attractive potential for the tail tail interactions.
lappend nb_interactions [list 1 1 lj-cos2 $lj_eps $lj_sigma $ljoffset 1.6 ]
===========================================================================================================
I checked my scripts but I couldn't find the mistake.
Could you help me with this issue?
Thanks a lot for your time.
Salvador
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