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Re: [lammps-users] Pressure tensor calculation under Drude Force field
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Re: [lammps-users] Pressure tensor calculation under Drude Force field


From: Steve Plimpton <sjplimp@...24...>
Date: Mon, 14 May 2018 07:41:01 -0600

Best for you to email the Drude contributors directly for this Q.
See src/USER-DRUDE/README.

Steve



On Fri, May 11, 2018 at 1:49 PM, Hyuntae Jung <hjung52@...107...> wrote:


Hello, 


Just to make sure, I try to understand the comments about pressure tensor calculation with drude particle systems on Lammps manual http://lammps.sandia.gov/doc/fix_langevin_drude.html

At the final stage, I would like to calculate shear viscosity using pressure tensor.

However, I try to know how Lammps calculate pressure tensor under Drude force field.


As the comment said, 
"Contrary to the alternative thermostating using Nose-Hoover thermostat fix npt and fix drude/transform, the fix_modify command is not required here, because the fix nph computes the global pressure even if its group is ATOMS. This is what we want. If we thermostated ATOMS using npt, the pressure should be the global one, but the temperature should be only that of the cores. That’s why the command fix_modifyshould be called in that case."

Does it mean that Lammps calculate kinetic term and virial term regardless of drude or atom groups to obtain pressure?
Here, in the purpose of calculation of pressure, kinetic term = sum_(i) m_i * v *v  where i should be just all particles including drude particles, right? 
Also, is the virial term calculated with all particles?

Thank you,

Hyuntae Jung

Chemistry Department

University of Wisconsin-Madison


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