[gmx-users] Inaccurate pressure readings

Justin A. Lemkul jalemkul at vt.edu
Thu Jan 20 23:09:03 CET 2011

Denny Frost wrote:
> I am running a variety of NPT simulations with polar, non-polar, and 
> ionic compounds.  Although my results for density agree well with 
> experimental values, the pressures I get from g_energy are off by 1 to 3 
> orders of magnitude.  In the log file, the pressure fluctuates around a 
> lot from -400 to 400 bar, which seems to be normal according to other 
> posts on this list, but the average (which is what g_energy gives me) is 
> not 1.0 bar, as I specified.  Does anyone know how to correct this problem?

What is the average value you're getting?  How long are your simulations?


> Pressure coupling parameters:
> Pcoupl              =  berendsen
> pcoupltype          =  isotropic
> tau_p                   =  1.0
> ref_p                   =  1.0
> compressibility     =  4.5e-5


Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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