Hi there,

I am doing simulations of a membrane protein,  and I am  trying to apply 
surface tension to the membrane in order to observe how  the protein respond to 
it.
I have several questions of how to apply a surface tension to a membrane

1, this is what I am using in my mdp file, could anyone comment on it? I am not 
sure if I am doing it correctly:

pcoupl                  = berendsen
pcoupltype              = surface-tension
tau_p                   = 5.0
compressibility         = 4.5e-5  4.5e-5
ref_p                   = 200    1.0

Is  my setup correct?  In the manual, it is mentioned that a accurate  enough 
compressibility for the z direction should be used. What value is  considered 
as accurate enough?
I noticed that in some papers, people  use "semiisotropic" for option 
"pcoupltype" and use a negative pressure  (such as - 80 bar) for "ref_p" 
option. In this way, a surface tension  is applied "in directly". Is th
is recommended? What is the advantage and disadvantage of this method?

2,  It is said that the surface tension converge slowly. Generally for a  
regular membrane constituted by POPC, how long does it take for the  surface 
tension to converge?

I tried so send this message  yesterday, but it seemed that it was not sent 
successfully. So I paste  it again, sorry for the inconvenience. 



Thanks very much for your help in advance. Any suggestions are highly 
appreciate!

Cheers,
Ruo-Xu
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