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Re: [lammps-users] Modelling solids and thermostatting them
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Re: [lammps-users] Modelling solids and thermostatting them


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Mon, 28 Aug 2017 09:11:39 -0400



On Mon, Aug 28, 2017 at 8:56 AM, Tir McDohl <tir.tenkai@...24...> wrote:
Hi LAMMPS Users,

I was wondering if any of you could give me some advice on how solids should be modelled in LAMMPS? I read in one of the mailing list threads that some people go about this by creating several slices: (1) An unmoving slice, where atoms are not integrated at all (these should be on either side of the simulation box?) (2) A slice that is thermostatted (e.g. Langevin) (3) and then a slice that is NVE integrated, and this slice is the 'slice of interest'.

​what you are describing is a typical setup for a slab system.​
 

Is the above the best way of modelling a generic solid? For example, would a good solid model, for looking at a steady state temperature profile, be: 1 2 3 2 1 (where the numbers correspond to the slice types above)? Do I need to consider adding other commands, like a fix spring/self command? The temperatures I aim to look at are no higher than 300K, and my solids don't need to be any special materials (though I've been inspired by some papers that try to model solid argon films). A solid with harmonic bonds between its atoms is sufficient - is there a particular way of modelling such a solid that you would advise using? Are there perhaps some specific academic papers that discuss this that I should look at?

​none of these are questions about LAMMPS. they are all about how to plan a simulation of your system of interest in general and thus apply to all MD codes.​
​how to plan your research is a topic for a discussion with your adviser/supervisor not this mailing list, which is focused on issues specific to the LAMMPS code.
from the looks of it, you need to do a much more thorough survey of the literature. for everything you are asking about, there should be plenty of examples in the published literature. a temperature profile like you describe is, for example, used in one of the several ways of computing thermal conductivity: ​http://lammps.sandia.gov/doc/Section_howto.html#howto-20  apart from that, it looks like you need to first get a better grasp on modeling (bulk) materials and their properties properly without any additional complications.

axel.

 

I hope you don't mind me asking such general questions! I look forward to hearing from you.

Have a good day,

Tir



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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.