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 <[email protected]> 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 <[email protected] > > <mailto:[email protected]>> 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 > > <[email protected] <mailto:[email protected]>> 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 > > >[email protected] <mailto:[email protected]> > > >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 > > [email protected] <mailto:[email protected]> > > http://pwscf.org/mailman/listinfo/pw_forum > > > > > > > > > > > > _______________________________________________ > > Pw_forum mailing list > > [email protected] > > 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 > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum >
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