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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
Graduate Research Assistant, Mechanical Engineering
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?

***********************************************
School of Mechanical Engineering
Sharif University of Technology
Tehran, Iran.
***********************************************

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
Graduate Research Assistant, Mechanical Engineering
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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