[Pw_forum] Smearing Problem

[paresh rout]

Sorry sir in the previous plot the energy difference was not per atom. So
here I am attaching the Corrected plot. My system contains 20 atom.

On Wed, Jul 1, 2015 at 6:09 PM, paresh rout <paresh.rout88 at gmail.com> wrote:

> 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
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>>
>
>
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