[Pw_forum] Smearing Problem

[Nicola Marzari]

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
>
>
>
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-- 

----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL