[Pw_forum] Smearing Problem
paresh rout
paresh.rout88 at gmail.com
Thu Jul 2 20:24:55 CEST 2015
Hello Sir,
The units are in mRy. I tried with halving and doubling the F-D smearing
value and the energy difference remains same (0.06mRy/atom) using largest
k-point sampling. Can I rely on this F-D smearing (0.00184) results now ?
I am also doing a convergent test on MV smearing with the largest k-point
sampling.
Kind Regards
Paresh
On Wed, Jul 1, 2015 at 8:18 PM, Nicola Marzari <nicola.marzari at epfl.ch>
wrote:
>
> Hi Paresh,
>
>
> all good - but are you sure the units are mRy? A difference of
> 0.06 mRy /atom is super small (11604K=1eV), so we are talking about
> 10K difference, lost in the noise of the errors of approximate functionals,
> entropic effects, etc...
>
> Anyhow, if you want the computational "truth" you could try halving or
> doubling the fermi-dirac smearing (or m-v, or m-p), using the largest
> sampling,
> and see if you get the same number.
>
> nicola
>
>
> On 01/07/2015 21:15, paresh rout wrote:
> > 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
> > <mailto: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 <mailto: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
> > >
> > >
> > >
> > > _______________________________________________
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> > >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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>
> --
>
> ----------------------------------------------------------------------
> 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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