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Re: [lammps-users] Calculate tail correction for EAM potential
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Re: [lammps-users] Calculate tail correction for EAM potential


From: rbasir <rbasir@...3833...>
Date: Tue, 22 Aug 2017 14:37:57 +0000

Actually tail correction for lj systems is in literature and without that I was getting false density and pressure in the system for different potential parameter so it has a physical reason.

No, in my implementation I just get the total potential energy from Lammps whenever I need it in my Monte Carlo calculation and assume it is a configurational energy and treat it like the potential energy plus tail correction energy in lj system. Is that wrong?

Thank you axel.


From: Axel Kohlmeyer <akohlmey@...24...>
Sent: Tuesday, August 22, 2017 10:04:04 AM
To: rbasir
Cc: Steve Plimpton; lammps-users@lists.sourceforge.net
Subject: Re: [lammps-users] Calculate tail correction for EAM potential
 


On Tue, Aug 22, 2017 at 9:46 AM, rbasir <rbasir@...3833...> wrote:
Thank you axel, so if I want to include longer range in my calculation I need to redesign EAM potential or there is another way to calculate that part of interaction without changing the current potential?

this is not my area of research. i have explained what i know.
 
And my second question is that my EAM potential is working for regular MD and I see a phase separation in a box, so can I conclude that the interaction beyond the cutoff has no physical meaning in my system When it's working in MD? Or they can be a game changer when it comes to Gibbs ensemble method?

​when a model is not considering interactions beyond a cutoff, that doesn't mean, there are none. it simply means that they are considered negligible or that they cancel out. for homogeneous(!) liquid metals, for example, that is a good approximation to assume that interactions cancel beyond a certain distance.

since gibbs ensemble is not my area of research i cannot tell you how this translates. in fact, your line of questioning suggests, that you need to validate whether your use of tail corrections for lj/cut interactions is actually giving you an improvement for a correct physical reason or just by accident. once you have explored and fully(!) understood that, it should be more clear how to address issues that you are seeing.

another question that comes to my mind is: does your implementation consider that EAM interactions are not pairwise additive? 

in conclusion, i think you need to start a conversation with your adviser/supervisor and dig deeper into the literature. this mailing list is focused on technical issues around LAMMPS. we usually don't have the time (or interest?) to provide advice on planning research projects.

​axel.​

 

Thanks,
Ramin

From: Axel Kohlmeyer <akohlmey@...24...>
Sent: Tuesday, August 22, 2017 9:34:37 AM
To: rbasir
Cc: Steve Plimpton; lammps-users@...396...sourceforge.net

Subject: Re: [lammps-users] Calculate tail correction for EAM potential
 


On Mon, Aug 21, 2017 at 1:22 PM, rbasir <rbasir@...3833...> wrote:
Thanks Steve, I wrote a code which coupled with lammps to perform Gibbs ensemble hybrid Monte Carlo and it works for lj system and for lj system I had to include energy beyond the cut off( tail correction) now I want to simulate liquid alloys and I'm wondering how I can calculate energy beyond the cutoff for eam potential. Is that possible?

let me rephrase what steve wrote: ​if a potential is going smoothly to zero at the cutoff, there cannot be a tail correction like it is computed for lj/cut and alike. the tail correction is computing the part of a potential that is truncated through the cutoff.

now, if you want to compute a long(er)-range interaction contribution for EAM, you have a completely new model.

​axel.​

 

Thanks,


From: Steve Plimpton <sjplimp@...24...>
Sent: Monday, August 21, 2017 1:17:56 PM
To: rbasir
Cc: lammps-users@...655....net
Subject: Re: [lammps-users] Calculate tail correction for EAM potential
 
There is no tail correction for EAM.  It goes smoothly
to 0.0 at the cutoff.

Steve

On Sun, Aug 20, 2017 at 8:14 AM, rbasir <rbasir@...3833...> wrote:
Dear all,

There is a command( pairmodify tail yes) which can calculate long-range correction for LJ potential but it does not work EAM potential. Does anyone know how to calculate tail correction for EAM potentials?

Thanks,
Ramin

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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.



--
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.