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Re: [lammps-users] NPAT Ensemble
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Re: [lammps-users] NPAT Ensemble


From: David Stelter <dstelter@...5214...>
Date: Mon, 23 Oct 2017 13:03:38 -0400

Hi Sina,

All the options you supplied are different, you should carefully read the fix npt documentation (http://lammps.sandia.gov/doc/fix_nh.html) and all options. The barostat keywords you are modifying allow you to set each component of the pressure tensor individually.

fix              fixnpt all npt temp 298.15 298.15 2000 x 0 0 2000 y 0 0 2000 z 98.6923 98.6923 2000 couple xy drag 20.0

This set the target pressure for the x and y component of the box to 0, and the z to 98.6923. The x and y components are coupled and hence scaled by the same amount during a barostat move.

fix              fixnpt all npt temp 298.15 298.15 2000 aniso 98.6923 98.6923 2000 couple xy drag 20.0

This sets the target pressure to 98.6923 for all components, otherwise same as above.

fix              fixnpt all npt temp 298.15 298.15 2000 z 98.6923 98.6923 2000 drag 20.0

This tells the barostat to only make moves in the z component with a target of 98.6923.

David

On Wed, Oct 18, 2017 at 8:37 PM, Sina Mirzaeifard <sina.mirzaeifard@...4591...> wrote:
Hello,

I'm having really hard time finding a way how to implement NPAT ensemble (constant normal pressure and cross sectional area) for ultimately calculating the surface tension obtained from the mechanical definition. I read the mail list and the manual, so tried many ways such as the command lines below but the cross sectional area will not stay fixed or the box length in z direction keeps increasing. I was wondering if anyone could help me with this issue and let me know if there is a specific way of applying NPAT ensemble in LAMMPS. I really appreciate the time and consideration.

fix              fixnpt all npt temp 298.15 298.15 2000 x 0 0 2000 y 0 0 2000 z 98.6923 98.6923 2000 couple xy drag 20.0

fix              fixnpt all npt temp 298.15 298.15 2000 aniso 98.6923 98.6923 2000 couple xy drag 20.0

fix              fixnpt all npt temp 298.15 298.15 2000 z 98.6923 98.6923 2000 drag 20.0


Cheers,
Sina

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--
David Stelter
Graduate Student
Department of Chemistry
Boston University