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Re: [lammps-users] Solid state materials combustion
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Re: [lammps-users] Solid state materials combustion

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Tue, 4 Jul 2017 11:42:08 -0400

On Mon, Jul 3, 2017 at 8:46 PM, renefbg <renefbg@...6901...> wrote:
> Sorry for such a simple question, but I am having trouble in simulating the
> decomposition/combustion/explosion of some materials, starting in solid
> state.
> The structure of the crystal/molecules is totally changed in the first
> iteraction.
> I am using ReaxFF and building the data file using VMD, after creating the
> molecule file using avogadro and then creating the crystal structure using
> packmol (basically I used the crystal lattice parameters and inserted a
> certain amount of molecules to achieve the near-experimental density). Maybe
> packmol is creating a high energy distribution?

if your system has a high potential energy, you should see it in your
thermodynamic output.
if that is high, you could run a minimization (as it standard
procedure in MD) as initial part of your equilibration.

another common beginner's mistake with reaxff, is to generate a data
file with bonds/angles/dihedrals etc. those are computed dynamically
and providing them explicitly is an error, as it will change the force
field interactions.

> I even tried to use the fix rigid command, but it keeps the material from
> decomposing over time.

finally, you have to carefully check the force field parameters. you
need a set that is specifically parameterized for your kind of system.
reaxff is very specific and the resulting parameter sets are not very


> Thanks for any suggestions.
> --
> Prof. Dr. Rene F. B. Gonçalves
> Departamento de Química
> Instituto Tecnológico de Aeronáutica
> Tel: +55 12 3947-6852
> Sec: +55 12 3947-5845
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Dr. Axel Kohlmeyer  akohlmey@...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.