[gmx-users] Question about phospholipid monolayer on a water/air interface...

[Sergio Garay]

Hi
 
My name is Sergio Garay, and I'm working on a simulation of a phospholipid 
monolayer on a water/air interface. To mimic that system I have constructed a 
rectangular box with a thick layer of water at the center, two monolayer of 
lipids (with their polar heads pointing toward water) at each side, an 
finally two thick vacuum layer a each side (I think, the air component could 
not be considered here due to the size of the simulation system)
I would like to make a constant Area calculation, to obtain the surface 
tension of the system. My questions is:

What is the more adecuate condition to do this?
 
Although the normal pressure would be 1 atm at the experimental condition, 
this pressure is not compatible with the vacuum in the simulation box unless 
the compressibility in the Z direction would be fixed at value 0.0 to keep 
the Z box dimension fixed.

1) Is it convenient to simulate at fixed volume (NVT)

or 

2) at the constant Area (x,y) ensemble with normal pressure 0 / 1 atm, normal 
compressibility equal 0.0, and x,y compressibilities equal 0 ? A kind of 
NPzAT ensemble

Is there a more appropiate alternative?


Thank you in advance

-- 
Sergio Garay
Facultad de Bioquimica y Cs. Biológicas
Santa Fe (3000) Argentina
Casilla de Correo