[Pw_forum] Smearing Problem

[paresh rout]

Thank you very much sir. That was a very helpful reply. Now I understand
 smearing. Just one more query, I did a convergence test with k-point
sampling  by fixing the F-D smearing value to 0.00184 and the energy
difference between C-type and G-type  seems to be converged (I have
attached the convergent test plot). If I understand your explanation
correctly then this result should also be reliable. Please let me know if I
am wrong.

 I will also do the convergent test with M-V(0.01) and the second solution
that you have suggested.
(The K-points grids are 8 8 6 , 10 10 8, 12 12 10, 14 14 12, previously I
was using 8 8 6)

Kind Regards
Paresh Chandra Rout
Research Scholar
INDIAN INSTITUTE OF SCIENCE EDUCATION AND RESEARCH, BHOPAL


On Wed, Jul 1, 2015 at 12:56 PM, Nicola Marzari <nicola.marzari at epfl.ch>
wrote:

>
>
> Dear Paresh,
>
>
> maybe this is easier to follow:
> http://theossrv1.epfl.ch/Main/ElectronicTemperature
>
> The main concept is that with very small smearing you need *a lot* of
> k-points
> to perform the correct Brillouin zone integrations - so with a 0.00184
> smearing
> you have a *large* error due to insufficient sampling, not a small error.
>
> Solution 1 - if you do not want to think, ever, in your life, use 0.01
> Ry of m-v
> or m-v smearing, and increase the k-point sampling until the difference
> in energy
> between G and C type is converged.
>
> Solution 2 - plot the energy difference between G and C as a function of
> smearing,
> for m-v smearing of 0.005, 0.010, 0.015, 0.020, 0.025, and with at least
> 3 or
> 4 k-point sampling. Use the discussion from
> http://theossrv1.epfl.ch/Main/ElectronicTemperature
> to understand what to do.
>
>                                 nicola
>
>
>
> On 30/06/2015 17:07, paresh rout wrote:
> > Dear all,
> > I am dealing with a transition metal oxide compound (ABO3), Where I use
> > cold smearing *m-v(0.02)* for geometry optimization and for total energy
> > calculation I use *f-d (0.00184*) at the final optimized structure. I
> > have calculated the total energy for various type of magnetic ordering
> > like (G-type, C-type). The total energy (SCF) for G-type and C-type are
> > in reverse ordering for different smearing technique (*G-type is the
> > ground state for* *MV smearing and C-type is the ground state for FD*).
> > But when I reduced the value of degauss of *MV to 0.008 *I got the same
> > ordering as FD.
> > I am very confused about the smearing technique . I have also read Prof.
> > Nicola's thesis about smearing but there I did not get rid  of my
> > confusion also I did not find about FD technique . Can anybody kindly
> > tell me about the right smearing technique which I can use for the spin
> > polarized calculation ? Any reply would be highly appreciated.
> >
> >
> > Kind Regards
> > Paresh Chandra Rout
> > Research Scholar
> > INDIAN INSTITUTE OF SCIENCE EDUCATION AND RESEARCH, BHOPAL
> >
> >
> >
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
> >
>
> --
>
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
> _______________________________________________
> Pw_forum mailing list
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