Dear Julien, what smearing did you have in mind? Have you tried raising the broadening?
Cheers, Fabrizio On Thu, 21 Feb 2019 at 12:19, Julien Barbaud <[email protected]> wrote: > Dear users, > > > I am new to QE, and trying to run a simple scf calculation on a CH3NH3PbI3 > crystal (semi-conducting material). I am using ultrasoft pseudopotentials > based on the exchange-correlation functionnal PBEsol. > > I set up a first input, with values of parameters inspired from literature > on the subject. However, I could not reach convergence after 100 > iterations. The estimated error was actually "exploding" to very high > values, indicating a serious problem. I tried several changes but was > unsuccessful: > > - varying plane-wave cutoff energy does not solve the problem (cf > attached ecut.png, giving the estimated error as a function of the number > of iterations. It is shown here only on the first 15 iterations as the > results pretty much only stall from there) > - varying cutoff energy for charge (cf ecutrho.png) > - taking larger k-point sampling (not shown) > - I also read that for metallic or "close to metallic conductors", > there might be problems with the first unoccupied states that can be solved > by adding a few empty bands. My system being a semi-conductor, I tried > adding additional bands using a m-p smearing but no improvement was found > (not shown) > > > The only change that I found effective was to reduce the mixing_beta > factor. > > > It effectively prevents the error from diverging to very large values, but > I still do not reach convergence, even after longer iterations. I tried > much smaller values of mixing beta which improves the final value of the > error, but I still cannot reach convergence on 100 iterations. As shown in > the mixbeta2_zoom.png, the error reduces to smaller values around > ~1e-5~1e-6, but it keeps stalling after a while. I do not observe a > well-converging behaviour for any value. > > > I attached the "default version" of my script on which the various > modifications described above have been independently performed. I obtained > the geometry from a CIF file in literature and checked it with > visualization software; it seems perfectly ok as far as I can tell. > > > Any insight on what I did wrong would be really helpful. I suspect a > shameful beginner mistake, but can not find it out. > > > Thanks in advance, > > Julien barbaud > > > P.S: this is my first time posting on this user list. Please let me know > if my question is not suitable for it, or can be improved either in its > content or presentation. I will gladly take any recommandation into account > in order not to negatively impact the quality of this user list ! > _______________________________________________ > users mailing list > [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users -- *Fabrizio Cossupostdoctoral fellow at APCTP (Asia Pacific Center for Theoretical Physics)*, Hogil Kim Memorial Building #501 POSTECH, 67 Cheongam-Ro, Nam-Gu, Pohang-si, Gyeongsangbuk-do, 790-784 (37673), Republic of Korea | .----. .----. .----. |---- .----. =========================== ,----| | | | | | | http://www.apctp.org/?JrgId=16 `----^ |----' `----' `----' |----' =========================== | |
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