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Re: [lammps-users] [EXTERNAL] Fwd: EAM/alloy cutoff with zbl spline
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Re: [lammps-users] [EXTERNAL] Fwd: EAM/alloy cutoff with zbl spline


From: "Thompson, Aidan" <athomps@...3...>
Date: Tue, 27 Jun 2017 16:27:25 +0000

pair_style hybrid/overlay is purely additive; it does not do splining, or rather splicing, of two potentials as a function of radial distance. This is not something that can be done in a general way in LAMMPS, because the splicing function must be carefully constructed to match the forms of the inner and outer functions. One specific case where this has been done is for Tersoff and ZBL:

 

http://lammps.sandia.gov/doc/pair_tersoff_zbl.html

 

It might be possible to code up a version of hybrid/overlay that splices together two strictly twobody pair styles using the same 1/(1+exp(-k(r-rc)) splicing function.  Making that work for manybody potentials like EAM would still present some complications.  

 

In order to address your specific problem, simpler solutions are:

 

1. Eliminate the discontinuity in the EAM potential itself.

or

2. Prevent the system from access the "very small separations" perhaps by using ZBL and pair hybrid/overlay to raise the energy of the system near the discontinuity.

 

Aidan

 

 

 

---------- Forwarded message ----------
From: Alexandra Adrych-Brunning <alex.adrych-brunning@...5193...>
Date: Fri, Jun 23, 2017 at 2:51 AM
Subject: [lammps-users] EAM/alloy cutoff with zbl spline
To: "lammps-users@lists.sourceforge.net" <lammps-users@lists.sourceforge.net>


Hi all, 

 

I have an EAM potential which has a discontinuity at very small separations which I thought could be removed by applying a ZBL at small separations using the pair_style hybrid/overlay. My current script looks like:

 

units metal

dimension 3

boundary p p p

atom_style atomic

 

atom_modify map array

atom_modify sort 0 0.0

variable    u uloop 100

 

pair_style hybrid/overlay eam zbl 0.0001 0.3 

pair_coeff * * eam Zr.eam.fs Zr Zr

  

pair_coeff zbl * * 40.0 40.0

 

However the discontinuity is not removed when the zbl is applied because no matter the zbl cutoffs, the discontinuity is always included.  

Is there a way instead which will spline the zbl to the eam at the cut off distance rather than overlaying the two?

 

Thanks in advance

Alex

 

 


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