[gmx-users] Pressure Fluctuations

[Mark Abraham]

On 16/03/11, Kavyashree M  <hmkvsri at gmail.com> wrote:
> Dear users,
> 
> Upon was trying to simulate an npt ensemble (protein in water),
> pressure was coupled using  parinello rahman system with tau_p = 2,
> tau_t = 1; compressibility 4.5e-5, type = isotropic.
> 
> (cut off scheme (vdw_type = switch; rvdw = 1.0; rvdw_switch = 0.9;
> 
> rcoulomb = 1.2; rlist = 1.2).
> 
> No matter what value of tau_p is used (0.5, 1, 2, 2.5, 3, 3.5), the pressure
> fluctuations are very drastic. I have gone through the mailing list regarding 
> this issue but could not come to any conclusion.
> 
> 
> Any suggestions are helpfull.
> 
> This is one of the statistics for pressure fluctuations.
> 
> Statistics over 500001 steps [ 0.0000 through 1000.0000 ps ], 1 data sets
> All statistics are over 100001 points
> 
> 
> Energy                      Average   Err.Est.       RMSD  Tot-Drift
> -------------------------------------------------------------------------------
> Pressure                    5.77629       0.99    398.013   -5.34218  (bar)
> 

Looks very normal. See http://www.gromacs.org/Documentation/FAQs number 3

Mark
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