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Re: [lammps-users] question about potential energy
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Re: [lammps-users] question about potential energy


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Wed, 18 Apr 2018 08:00:00 -0400

On Wed, Apr 18, 2018 at 6:19 AM, ehsan gowdini <ehsangowdini@...24...> wrote:
> Hi all user
>
> in my simulation I use the EAM potential for metal-metal interaction
> and Lennard-Jones potential for carbon-metal interaction
>
> I use these command for them
>
>
> 1)
> pair_style      eam
> pair_coeff 2*2 2*2 Au_u3.eam
>
> pair_style      lj/cut 14.0
> pair_coeff * * 1 1
> pair_coeff 1 1 0.10492547 1.7155
> pair_coeff * * 1 2
> pair_coeff 1 2 0.048427138 1.41964710735663
>
>
> 2)
> pair_style     hybrid lj/cut 14.0 eam
> pair_coeff      2*2 2*2 eam Au_u3.eam
> pair_coeff      1 2 lj/cut 0.048427138 1.41964710735663
> pair_coeff      1 1 lj/cut 0.10492547 1.7155
>
>
> simulation done at 298 Kelvin
> but in both of two way , metal crystal being vapor
>
> when i look at the output file I see the potential energy is very high
> such 1192000
>
> what and where is my mistake?

since you only provide a small part of your input, you force people to
guess and you cannot expect reliable responses. most likely, there are
other problems with your input deck.

entry 1) is flat out garbage.

the LJ parameters for entry 2) don't look right either. they appear to
be in kcal/mol instead of eV and the sigma values don't look
reasonable either.
based on seeing such basic errors already on something that is this
simple to get right, there are good chances, that there are many more
problems.
MD simulations follow the GI-GO (= garbage in, garbage out) principle,
so you have to get *everything* right, to have a meaningful
simulation. since you seem to have trouble with a multi-component
system, it is strongly advised to try and set up each component in a
separate simulation first and figure out how to do this to reproduce
already published data for the potential parameters in use.

axel.

> best
>
> Ehsan
>
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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.