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Re: [lammps-users] Granular package: gran/hooke
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Re: [lammps-users] Granular package: gran/hooke


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Wed, 18 Apr 2018 08:40:29 -0400

On Tue, Apr 17, 2018 at 8:10 PM, Vinay Vaibhav <vinayv@...6701...> wrote:
>
> Hi,
>
> I am doing some testing with the granular package. I take a bunch of
> spherical particles in a box.
>
>
> atom_style      sphere
> boundary        p p p
> newton          off
> comm_modify     vel yes
>
> region          box block 0 81 0 81 0 81 units lattice
> create_box      1 box
> create_atoms    1 random 200000 35418 box
>
> set             group all diameter 1
> set             group all mass 1
>
>
> Then I use gran/'hooke pair style but I keep only spring part of the normal
> force, others are set to zero.
>
> pair_style      gran/hooke 200000 NULL 0.0 NULL 0.0 0
> pair_coeff      * *
>
> I run it with nve/sphere and expect the energy of the system to be
> fluctuating around some mean value because the dissipative part of the force
> is zero. But I observe a systematic increase in the energy of the system.
>
> timestep        0.0001
> fix             1 all nve/sphere
> thermo          1000
> run             10000000
>
> Can anyone give me some explanation for this? Am I making any mistake
> somewhere?

have you tried a smaller time step?
non-conservation of energy is frequently caused by using too large a time step.

axel.

>
> logfile and plot of the energy are attached.
>
>
> With thanks and regards,
>
> Vinay Vaibhav
> Ph.D. Student, Theoretical Physics
> The Institute of Mathematical Sciences Chennai, India
>
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-- 
Dr. Axel Kohlmeyer  akohlmey@...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.