There is another easier solution but I have never tested. The default startingwfc is "atomic + random", instead one could try to use "random".
=================== Dr. Xiaochuan Ge (Giovanni) Center for Functional Nanomaterials Brookhaven national laboratory =================== On 3 February 2015 at 08:49, Pu ZHANG <[email protected]> wrote: > Dear all, > > I'm just curious about Xiaochuan's solution. It would be Interesting and > useful to be able to specify the initial configuration in such a flexible > way. As I understand from experience in other codes, it's trivial to set up > the occupation for the whole system, however rather than for separate > parts. > > Is there a way to make this setting? > 2015 年 2 月 3 日 下午 9:38于 "xiaochuan Ge" <[email protected]>写道： > > Dear Sergi Vela, >> >> I have encountered similar problems before. To solve your trouble I think >> the main question is: what is the converged electronic configuration you >> are expecting? >> >> I notice that your system is made by a gold slab plus a C2S3N3 molecule. >> The latter being isolated contains odd number of electrons. I believe if >> you run the ground-state calculation for only the C2S3N3 molecule without >> special care you will end up with similar problems with convergence. Using >> smearing does not solve your problem is probably because the band gap of >> C2S3N3 is too large for the smearing parameter you used to make a >> difference. >> >> The trick is, if somehow C2S3N3 can take one electron from the slab, then >> an even electron configuration can be achieved for the molecule, and most >> probably you will achieve the convergence. However, the initial electron >> configuration is generated based on the overlap of atomic orbitals. Since >> the molecule is pretty far away from the metal slab, a large barrier may >> hinder the electron from metal to transfer to the molecule. Therefore >> during the SCF iteration the system can not find its energy minimum. >> >> I have some suggestions that you may want to try. First, you may want to >> put the molecule closer to the slab, so the barrier between the initial >> electronic configuration and the reasonable final configuration is low >> enough for SCF to overcome. Second, you could try to set the initial >> configuration by hand, say let the system start with ( C2S3N3 - ) + ( Slab >> + ), I believe this is possible in QE. Third, maybe you can add a little >> magnetic filed to breakdown the degeneracy of spin up and down. >> >> Hope this can solve your problem! >> >> =================== >> Dr. Xiaochuan Ge (Giovanni) >> Center for Functional Nanomaterials >> Brookhaven national laboratory >> =================== >> >> On 3 February 2015 at 08:02, Sergi Vela <[email protected]> wrote: >> >>> Dear Guido and Giuseppe, >>> >>> Thank you both for your replies. >>> >>> The structure should be ok, it represents an organic molecule between 2 >>> gold electrodes. You should get something like the image I attach (do >>> you?). It is a rather standard scheme, as you may also see in: >>> >>> http://pubs.acs.org/doi/abs/10.1021/ja2090096 >>> >>> although my structure is simplified for testing. >>> >>> I don't know whether ibrav=0 is strictly necessary but, anyway, it >>> should not affect the outcome of the calculation, right? >>> >>> I have tested other k-point meshes without improvement. Anyway, I'll try >>> denser meshes together with Giuseppe's suggestions and let you know the >>> outcome. >>> >>> Cheers, >>> Sergi >>> >>> 2015-02-03 13:56 GMT+01:00 Giuseppe Mattioli < >>> [email protected]>: >>> >>>> >>>> Dear Sergi >>>> It seems that you bounce between more than one electronic configuration >>>> at every scf step. This is far from uncommon in the case of molecular open >>>> shell systems. :-( >>>> I can add one or two things to Guido's good advice. >>>> >>>> > I've tried several tricks to try to improve electronic structure's >>>> > convergence. Changing the 'mixing_beta', the 'type of mixing', >>>> removing the >>>> > smearing, >>>> >>>> Use always the more robust gaussian smearing (at least 0.01 Ry, but >>>> also more if you struggle for convergence) for geometry optimizations. If >>>> it does >>>> not converge, then m-p and m-v will also fail 99.9% . You can use other >>>> schemes after you tamed the system. Reduce also the mixing_beta down to >>>> 0.05 >>>> or 0.02 (with davidson). >>>> >>>> Maybe your starting configuration is horribly unlucky. Try (carefully) >>>> to use something like >>>> >>>> conv_thr=1.0d-5~1.0d-6 >>>> electron_maxstep=50~100 >>>> scf_must_converge=.false. >>>> >>>> and see if your convergence problem improves after few bfgs steps >>>> without showing unphysical behavior. >>>> >>>> If your SOMO is higher than the Ag Fermi energy, then there is probably >>>> no way to have an integer value for the magnetization of the system because >>>> of >>>> the molecule-to-surface charge transfer. You may try not to bias the >>>> tot_magnetization variable. >>>> >>>> Finally, ecutwfc=25.0 seems a bit too low. It could be a source of >>>> instability. I would use something around 35/280 Ry for ecutwfc and >>>> ecutrho. >>>> >>>> HTH >>>> Giuseppe >>>> >>>> >>>> On Tuesday, February 03, 2015 10:57:23 AM Sergi Vela wrote: >>>> > Hi all, >>>> > >>>> > I'm having a lot of troubles in modeling the adsorption of molecules >>>> on >>>> > surfaces. I've quite a lot of experience with QE when working with >>>> crystals >>>> > made of open-shell molecules but I'm not familiar with the >>>> description of >>>> > metal surfaces. >>>> > >>>> > First of all, I'm using Qespresso v.5.1.1 >>>> > >>>> > I succeed in simulating 4 layers of a 111 Gold surface with Quantum >>>> > Espresso (QE). However, using the same surface and unit cell, when I >>>> > include a magnetic (open-shell) molecule on top of that surface, even >>>> if >>>> > its far away from it, I cannot reach convergence. I'm 99% sure that >>>> the >>>> > input is fine in terms of the unit cell definition (see input file >>>> > attached) and the problem is just the convergence of the electronic >>>> > structure. >>>> > >>>> > I believe the problem is the fact that the system is highly >>>> inhomogeneous >>>> > as it has a metal surface and an open-shell molecule. I take as an >>>> example >>>> > the smearing, since, although it is mandatory when modeling the metal >>>> > alone, it seems to hinder the description of an open-shell molecule. >>>> > Originally, I used methfessel-paxton smearing with a 'degauss' of 0.2 >>>> eV. >>>> > The convergence seems to be even worse as the value is increased, and >>>> > changing the type of smearing doesn't help neither. >>>> > >>>> > I've tried several tricks to try to improve electronic structure's >>>> > convergence. Changing the 'mixing_beta', the 'type of mixing', >>>> removing the >>>> > smearing, switching to 'cg' algorith, increasing number K points ... >>>> all of >>>> > them with identical output (take Summary.out as an example of the >>>> typical >>>> > evolution of the SCF energy, you'll see that is awful). >>>> > >>>> > Anyone has experience on modeling such king of systems? >>>> > >>>> > Any help is appreciated, thanks in advance >>>> > >>>> > Dr. Sergi Vela, >>>> > University of Strasbourg, France. >>>> >>>> ******************************************************** >>>> - Article premier - Les hommes naissent et demeurent >>>> libres et ègaux en droits. Les distinctions sociales >>>> ne peuvent être fondèes que sur l'utilitè commune >>>> - Article 2 - Le but de toute association politique >>>> est la conservation des droits naturels et >>>> imprescriptibles de l'homme. Ces droits sont la libertè, >>>> la propriètè, la sùretè et la rèsistance à l'oppression. >>>> ******************************************************** >>>> >>>> Giuseppe Mattioli >>>> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA >>>> v. Salaria Km 29,300 - C.P. 10 >>>> I 00015 - Monterotondo Stazione (RM) >>>> Tel + 39 06 90672836 - Fax +39 06 90672316 >>>> E-mail: <[email protected]> >>>> http://www.ism.cnr.it/english/staff/mattiolig >>>> ResearcherID: F-6308-2012 >>>> >>>> _______________________________________________ >>>> Pw_forum mailing list >>>> [email protected] >>>> http://pwscf.org/mailman/listinfo/pw_forum >>>> >>> >>> >>> _______________________________________________ >>> Pw_forum mailing list >>> [email protected] >>> http://pwscf.org/mailman/listinfo/pw_forum >>> >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum >
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