Re: [potfit-users] Inconsistent cut-off in the embedding functions after fit

[Sayan S. <say...@br...>]

Hi Dr. Daniel,

Thanks for you response. Quite understandably you have a busy schedule and
tad bit delays are absolutely okay.

So to explain the problem a bit more, I have attached my parameter file, my
initial potential, my final potential and the log file which shows the
issues. Below I also explain the problem a bit in detail if it helps you.

If you look at the last 3 functions in both the endpot and startpot (the
embedding functions) (a Zr-Cu-Al system).

Startpot:

I have used the tabulated format 3, for the embedding functions I have 11
points equally spaced between 0 and 1 (as indicated on the top of the file).

Endpot:

The output is in tabulated format 4, here you see the last 3 x values in
the (x,y) pair in the embedding functions is not same

8.9343021666604872e-01 -3.6918050791576595e+00

9.0418686713284180e-01 -3.2943141771239048e+00

9.9999999999999978e-01 -5.9976263285993658e+00

I think this is not allowing the lammps potential to be written as
mentioned in the log file.

Potential in format 3 written to file Zr-Cu.endpot
Potential plotting data written to Zr-Cu.plot
[WARNING] LAMMPS potential cannot be written due to inconsistent cutoff
distances!
[WARNING] Embedding function 10 is cut off at 0.904187 instead of 0.893430.

Again, thanks for your inputs.

Best
Sayan

Sayan Samanta
Ph.D candidate
Materials Science | School of Engineering
Brown University
Providence, RI 02912 USA
+1 (401) 699-1340


On Thu, Mar 25, 2021 at 12:11 PM Daniel Schopf <sch...@gm...> wrote:

> Hi Sayan,
>
> I am sorry for the delayed answer.
>
> Please note that writing LAMMPS potentials is a not well
> tested feature, especially for tabulated potentials. And potfit
> allows certain freedoms which are not supported by LAMMPS,
> so this makes converting the potentials a little bit tricky.
> If you find any issues please let us know.
>
> I am not sure what you are describing here. Maybe sharing you
> in- and output files might help me better understand your situation.
>
> Also I am not aware of any tricks for tabulated potentials. For analytic
> potentials there is something like a cutoff function but not for tabulated
> potentials. You can set the gradient at the cutoff (which you probably
> did) to
> 0 and that should usually give you something like a vanishing potential
> at the cutoff distance.
>
> Rescale is definitely something to help fix the gauge degrees of freedom
> and
> the punishments also tries to do this. They are not mutually exclusive,
> even
> when rescaling is enabled we still place some restrictions on the potential
> and punish it for bad behavior.
>
> Daniel
>
>
> Am Montag, 15. März 2021, 21:01:43 CET schrieb Sayan Samanta:
> > Hi,
> >
> > I'm running potfit-20201014 with mpi, stress and rescale enabled. At the
> > end of the fit, potfit is unable to write LAMMPS potential because of
> > inconsistent cut-offs.
> >
> > I checked the final potfit potential and indeed the last x value for the
> > embedding function is not the same (not 1.0).  I began with the starting
> > potential that did not have that inconsistency, in fact, another fit
> > without the rescale option worked fine.
> >
> > Did I do something wrong? I could share the output files that might help
> > you diagnose a fix. Also is that 0 energy value at a large distance (for
> > the pair and transfer function) a trick to ensure smooth cut-off to zero
> in
> > the tabulated case?
> >
> > Lastly, am I correct to think that both rescale and punishment are
> > different tactics to fix the gauge of the potential and that if we are
> > rescaling we don't need punishment and vice versa?
> >
> > Best
> > Sayan
> >
> > Sayan Samanta
> > Ph.D candidate
> > Materials Science | School of Engineering
> > Brown University
> > Providence, RI 02912 USA
> > +1 (401) 699-1340
>
>
>
>
>
>
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