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Re: [lammps-users] Using Irving-Kirkwood formalism for pressure

# Re: [lammps-users] Using Irving-Kirkwood formalism for pressure

 From: Eric Murphy Date: Wed, 8 Nov 2017 13:29:21 -0600

There's no magic bullet for converging statistics, if you don't want to or can't change physics, systems size, etc. The only way to do that is with more samples.  I typically run multiple realizations for transient systems.  You can't rely on the ergodic hypothesis for all things.

Note that theses are just questions about how to compute expectations - not actually LAMMPS Q's.  Best of luck.

Regards,
Eric Murphy
Iowa State University

On Wed, Nov 8, 2017 at 12:22 PM, wrote:
Yes i want to compute pressure but my system is transient and i can't use time average ensemble for computing pressure.
I cant find any method for dealing this.
Do you know any method or someone could help?

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School of Mechanical Engineering
Sharif University of Technology
Tehran, Iran.
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From: Eric Murphy <murphyericjames@...24...>
To: elina9015@...47....
Cc: "lammps-users@...396...sourceforge.net" <lammps-users@...396...sourceforge.net>
Sent: Wednesday, 8 November 2017, 21:45:38
Subject: Re: [lammps-users] Using Irving-Kirkwood formalism for pressure

You might want to elaborate on whether you want to calculate pressure (in which case see the manual - common topic on the list as well) or control some sort of pressure drop.

Regards,
Eric Murphy
Iowa State University

On Tue, Nov 7, 2017 at 1:35 PM, wrote:
Hello users
I want to measure pressure for a transient flow.
In the following paper mentioned that Irving-Kirkwood formalism can be used with the peculiar velocity as the molecular velocity minus the
streaming velocity at the molecular position and averaging in short period.
"Molecular dynamics simulation of a pressure-driven liquid transport process in a cylindrical nanopore using two self-adjusting plates"
Is this possible for a transient flow?
I did not see this kind of work in any publications.
Any help for determining pressure in a transient flow will be appreciated.

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