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Re: [lammps-users] Temperature surges simulating calcite surface with water
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Re: [lammps-users] Temperature surges simulating calcite surface with water


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Thu, 26 Apr 2018 09:29:39 -0400

On Thu, Apr 26, 2018 at 7:13 AM, Ruiz Hernandez, S.E. (Sergio)
<s.e.ruizhernandez@...4949...> wrote:
> Dear Lammps users,
>
> I have been trying to simulate a surface of calcium carbonate surface in contact with water. Using the force field published by Raiteri et al in J. Phys Chem C 2015, 119, 24447-24458 DOI:10.1021/acs.jpcc.5b07532
> The version of Lammps I am currently using for testing is the Ubuntu binary, obtained in ppa:gladky-anton/lammps

that is a useless description. as explained in (the beginning of) the
LAMMPS manual, the version of LAMMPS is the date printed at the
beginning of every run.

> The structure data file was created using Molteplate. The dynamics computation details are the same as published in the above mentioned paper (as accurately as described in the article) The full input files are attached.

[...]

> I have been searching the mailing list, but finding working input files of surfaces is a bit difficult. I have also scanned the manual, changed the thermostat to Berendsen, that one controls the temperature very well, but similar system was published before with Nosé-Hoover. The paper cited uses npt, I have done so as well with the same results, but I have tried to reduce the problem
> I would like some advice regarding the jump in the temperature from 300 K to over 1000K. It will gradually return to 300K but that initial surge causes huge relaxations that are not expected nor seeing with other codes.

are you referring to running the *exact same* input geometry and force
field with a different MD software?

> I have tried other systems Ca, CO3 ions in solution. The temperature behaves very well in that case, but as a calcite surface is being published before, made me think I am missing something important in my input file.

you seem to be missing that a) almost any simulation protocol needs
include some steps of equilibration, and b) that many times initial
geometries may not be fully in accord with the force field used, even
if they represent experimental structures.

thus for many complex systems, simulation protocols have to start with
checks for overlaps and high potential energy areas, usually followed
minimization/geometry optimization, followed by a
equilibration/thermalization MD runs. for complex systems and delicate
structures, multiple minimizations alternating with short
equilibration runs may be needed, often also for each subsystem
separately.

if you have a polar surface in contact with a polar liquid, it is
*extremely* likely, that there are high potential energy spots where
the two subsystems are in contact, since the tool you are using to
construct the system does not no anything about the strength of the
interactions between the two systems.

furthermore, before starting a simulation with a multi-component
system, you should validate your force field parameter and geometry
input by simulating each component separately and verify, that there
are no typos or unit conversion errors or geometry mistakes.

at this point i do feel a bit like a broken record, since i seem to be
giving this kind of advice and suggestion regularly on this mailing
list, so perhaps you need to widen your scope of search through the
mailing list archives a bit.

axel.

>
> Best regards,
> Sergio
>
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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.