[gmx-users] compressibility

[Alex]

Dear all,
As you know the compressibility for water at 1 atm and 300 K is 4.5e-5 [bar
-1], I wonder how to choose proper compressibility for other materials? I
have two types of polymer inside water.
Also, I see sometimes the compressibility is indicated by one, two or three
number in the form of "compressibility  =  C1   C2   C3, then if those C1,
C2 and C3 are the compressibility in three geometrical directions of x,y,z
for the whole system, or just the compressibility for three type of
material existing in the system?
Thank you.
Alex