[gmx-users] time constants for the Parrinello-Rahman/nose-hoover coupling

[Erik Lindahl]

Hi,

Yes, you should. As I think we write somewhere in the manual or mdp  
file documentation, for Berendsen coupling the time constant refers  
to the exponential relaxation time, while for N-H or P-R they  
correspond to the period of the fluctuations between the system and  
reservoir. Typically I would set them 4-5 times longer than the  
Berendsen values.

Cheers,

Erik


On Oct 21, 2007, at 5:35 PM, Hwankyu Lee wrote:

> Dear GMX-users,
>
> I'm simulating lipid bilayer, and since fluctuation is important  
> for the study of undulation and area compressibility (Ka), I'm also  
> applying the Parrinello-Rahman and nose-hoover for the pressure and  
> temperature couplings. When I use the Berendsen, time constants are  
> like below.  When I use the PR, do I need to change time  
> constants?  Thank you for your time and help in advance.
>
> ----------------
> tcoupl                   = Berendsen
> ; Groups to couple separately = tc-grps                  = DPP W ;  
> Time constant (ps) and reference temperature (K) =  
> tau_t                    = 0.5 0.5
> ref_t                    = 323  323
> ; Pressure coupling      = Pcoupl                   = Berendsen  
> Pcoupltype               = Semiisotropic
> ; Time constant (ps), compressibility (1/bar) and reference P (bar)  
> = tau_p                    = 1.2   1.2 compressibility          =  
> 5e-5  5e-5   ref_p                    = 1.0 1.0 ------------------
>
> best,
> Hwankyu.
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