[Wien] Supercell calculation is not converging

Mon Sep 5 19:14:03 CEST 2011

Dear Laurence Marks Sir,

                   Thank you very much for your response. I have understood
what you want to say.

with best regards,

2011/9/5 Laurence Marks <L-marks at northwestern.edu>

> Check the confidence levl, e.g. t-test (i am not an expert with this
> package). Xrd Reitfeld is as susceptible to GIGO as DFT.
> On Sep 5, 2011 11:58 AM, "shamik chakrabarti" <shamikphy at gmail.com> wrote:
> > Dear Laurence Marks Sir,
> >
> > Yes this is an oxide and it is an insulator and probably I have made it
> > a metal by creating *cationic vacancies*. Sir I will let you know the
> detail
> > after checking it from case.output2. But Sir, please forgive my
> curiosity, I
> > could not wait to ask you and also going a bit away from wien2k
> questions:
> > 1) Sir the goodness of fit (GOF) obtained from Rietveld analysis done
> > through XPERT Highscore plus : 1.0038
> > and except this data we do not have any other proof to show that it
> > really have cationic vacancies.
> > Then Sir according to you we can not trust this data (considering GOF)
> > only to consider cationic vacancies?
> >
> > With best regards,
> >
> >
> >
> > On Mon, Sep 5, 2011 at 9:31 PM, Laurence Marks <L-marks at northwestern.edu
> >wrote:
> >
> >> Follow the science, not the DFT.
> >>
> >> 1) Unless you have a large grain size and synchotron data I really
> >> wonder about the logic of removing 1 atom in a 2x1x1 supercell.
> >> Particularly if this is an oxide, have you made it a metal whereas it
> >> should be an insulator? Does the fit pass significance tests etc? Do
> >> you have other data that implies vacancies?
> >> 2) In terms of the DFT, I expect that you have made it a metal which
> >> is harder to converge than an insulator. Check in case.output2 in both
> >> cases (a quick, pseudo DOOS). If it really does have vacancies, you
> >> might need more than 7 kpts, and I suggest using TEMPS.
> >>
> >> 2011/9/5 shamik chakrabarti <shamikphy at gmail.com>:
> >> > Dear wien2k users,
> >> > I have performed a 56 atom / unit cell calculation for a
> >> > ferrimagnetic material. It was well converged both in energy and
> charge
> >> by
> >> > 60 iterations. 14 K points were used for this calculation. Then I have
> >> > generated a 2x1x1 supercell having 112 atoms / supercell. This was
> done
> >> to
> >> > achieve better experimental model as obtained through Rietveld
> analysis.
> >> > From Rietveld analysis it was also seen that for 112 atoms we can
> >> consider a
> >> > cation (Fe) vacancy and we have generated it by deleting one Fe atom
> from
> >> > the supercell. Final structure, hence, contains 111 atoms and all
> other
> >> > occupancies at different lattice sites are well matched with Rietveld
> >> > analysis of experimental XRD. I am using 2 k points for this 111 atom
> >> > supercell. But even after 60 iterations the convergence achieved are
> as
> >> > follows:
> >> > cc: 0.234... cc was set to 0.001
> >> > ec: 0.063... ec was set to 0.0001
> >> > Sir, my question are:
> >> > 1) As the supercell is merely an extension of the 56 atoms unit cell
> with
> >> > more accurate values of atomic occupancies as in the experimental
> >> structure,
> >> > why it should at all taking so much time to converge?
> >> > 2) We have created one defect by creating a Fe vacancy...is it that
> the
> >> > structures having defect take more time to converge?...but as far as
> our
> >> > analysis until now..the structure should have one Fe vacancy per 112
> >> > atoms...
> >> > 3) As we have obtained converged solutions for 56 atom cell by using
> 14 k
> >> > points..is it that we should use 7K points for 111 atom supercell
> >> > calculation?..is 2 K points are actually small in order to achieve
> >> > convergence of this structure?
> >> > Any response in this regard will be very helpful for us. Thanks in
> >> advance.
> >> > with regards,
> >> >
> >> > --
> >> > Shamik Chakrabarti
> >> > Senior Research Fellow
> >> > Dept. of Physics & Meteorology
> >> > Material Processing & Solid State Ionics Lab
> >> > IIT Kharagpur
> >> > Kharagpur 721302
> >> > INDIA
> >> >
> >> > _______________________________________________
> >> > Wien mailing list
> >> > Wien at zeus.theochem.tuwien.ac.at
> >> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >> >
> >> >
> >>
> >>
> >>
> >> --
> >> Laurence Marks
> >> Department of Materials Science and Engineering
> >> MSE Rm 2036 Cook Hall
> >> 2220 N Campus Drive
> >> Northwestern University
> >> Evanston, IL 60208, USA
> >> Tel: (847) 491-3996 Fax: (847) 491-7820
> >> email: L-marks at northwestern dot edu
> >> Web: www.numis.northwestern.edu
> >> Research is to see what everybody else has seen, and to think what
> >> nobody else has thought
> >> Albert Szent-Gyorgi
> >> _______________________________________________
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> >> Wien at zeus.theochem.tuwien.ac.at
> >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >>
> >
> >
> >
> > --
> > Shamik Chakrabarti
> > Senior Research Fellow
> > Dept. of Physics & Meteorology
> > Material Processing & Solid State Ionics Lab
> > IIT Kharagpur
> > Kharagpur 721302
> > INDIA
>
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> Wien at zeus.theochem.tuwien.ac.at
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>
>

-- 
Shamik Chakrabarti
Senior Research Fellow
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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