[gmx-users] surface tension calculation in g_energy

2007-10-24 Thread Bo Zhou
Hi all,

   I use the option #Surf*SurfTens in g_engery to calculate the surface
tension, but I find that I really do not know how it works after I get some
inconsistent results compared with the calculation using the formula gamma
= 0.5*(Pzz - (Pxx+Pyy)/2) * Lz ( there are two surfaces here and the
surfaces in normal to the Z-axis).

 

Energy  Average   RMSD Fluct.  Drift
Tot-Drift


---

#Surf*SurfTen1136.52557.05   2557 0.00852598
51.1559

 

==  ###  ==

  A V E R A G E S  

==  ###  ==

   Pressure (bar)

   -1.93061e+02   -6.88599e-01   -1.66823e-02

   -6.84564e-01   -1.93953e+02   -2.93803e-02

7.79006e-03   -6.97915e-03   -9.87987e+01

 

The #Surf*SurfTens gives a value 568.25 bar*nm, and gamma = 0.5*(Pzz -
(Pxx+Pyy)/2) * Lz gives a value 473.54 bar*nm. Please give me some
suggestions about the inconsistency. Thanks in advance.

 

 

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Re: [gmx-users] surface tension calculation in g_energy

2007-10-24 Thread David van der Spoel

Bo Zhou wrote:



Hi all,

   I use the option “#Surf*SurfTens” in g_engery to calculate the 
surface tension, but I find that I really do not know how it works after 
I get some inconsistent results compared with the calculation using the 
formula “gamma = 0.5*(Pzz - (Pxx+Pyy)/2) * Lz” ( there are two surfaces 
here and the surfaces in normal to the Z-axis).


 

Energy  Average   RMSD Fluct.  Drift  
Tot-Drift


--- 



#Surf*SurfTen1136.52557.05   2557 0.00852598
51.1559


 


==  ###  ==

  A V E R A G E S  

==  ###  ==

   Pressure (bar)

   -1.93061e+02   -6.88599e-01   -1.66823e-02

   -6.84564e-01   -1.93953e+02   -2.93803e-02

7.79006e-03   -6.97915e-03   -9.87987e+01

 

The “#Surf*SurfTens” gives a value 568.25 bar*nm, and “gamma = 0.5*(Pzz 
- (Pxx+Pyy)/2) * Lz” gives a value 473.54 bar*nm. Please give me some 
suggestions about the inconsistency. Thanks in advance.


How did you calculate it? Did you divide the average pressures by the 
average box length? Or did you compute gamma for each step and average 
that (this is automatically done in the simulation and stored in the 
energy file). The two ways of computing are not the same.


--
David van der Spoel, Ph.D.
Molec. Biophys. group, Dept. of Cell  Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:  +46184714205. Fax: +4618511755.
[EMAIL PROTECTED]   [EMAIL PROTECTED]   http://folding.bmc.uu.se
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