Re: NPT ensemble with Periodic boundary condition

From: Dhiraj Srivastava (dhirajks_at_gmail.com)
Date: Wed Oct 25 2006 - 01:40:11 CDT

Hi all
      I am running my simulation in NPT ensemble. parameters and values for
pressure control are -
#Berendsen Pressure control
useGroupPressure yes
useFlexibleCell no
BerendsenPressure on
BerendsenPressureTarget 1.01325
BerendsenPressureCompressibility 4.57E-5
BerendsenPressureRelaxationTime 100
BerendsenPressureFreq 10

after about 500 timestep i am getting error message

ERROR: Step 10140 cell rescaling factor limited.

what may be the reason for this error? is this related to compressibility or
relaxation time?

Thanks for help.
Dhiraj

On 10/24/06, Peter Freddolino <petefred_at_ks.uiuc.edu> wrote:
>
> Hi Dhiraj,
> you may want to have a look at the NAMD documentation on pressure
> controls ( http://www.ks.uiuc.edu/Research/namd/2.6/ug/node32.html);
> you'll note that to have an NPT simulation periodic boundary conditions
> are *required*; otherwise there isn't a defined volume to use for
> pressure control. It is possible to use NPT for equilibration and NVE
> for production runs, which can avoid having a bad volume in your
> constant volume simulation.
> Peter
>
> Dhiraj Srivastava wrote:
> > Hi all
> > can i use periodic boundary condition when i am running my
> > simulation in NPT ensemble? if not then how could i set grid size for
> > PME calculation? and also could i equilibrate my system in NPT
> > ensemble and run my simulation in NVE ensemble after equilibration?
> >
> > thanks for help.
> >
> > --
> > Dhiraj Kumar Srivastava
> > Department of Chemistry
> > University of Missouri-Columbia
> > MO, 65211
> > Ph. no. 001-573-639-0153
>

-- 
Dhiraj Kumar Srivastava
Department of Chemistry
University of Missouri-Columbia
MO, 65211
Ph. no. 001-573-639-0153

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