Dear Giovanni, Thank you very much. It helps a lot.
Best, Reza On Wed, May 13, 2015 at 3:25 AM, Giovanni Cantele < [email protected]> wrote: > > > On 13 May 2015, at 02:41, reza vatan <[email protected]> wrote: > > > > Dear QE users, > > > > I'm trying to optimize a Silicon slab structure with 13 atomic layers in > each slab (attached file), but so far I have no success in optimizing > because of convergence problem in SCF cycle. Does any one know who I can > fix the problem. > > > > Many thanks, > > Reza > > <si-rel.in>_______________________________________________ > > Pw_forum mailing list > > [email protected] > > http://pwscf.org/mailman/listinfo/pw_forum > > > As far as I understand you are dealing with the Si(100) surface, aren’t > you? > > In the case, you might want to passivate the two sides of the slab with > hydrogens. If not, dangling bonds that necessarily appear can be more > difficult to converge. Also, consider that for that surface, surface Si > atoms are known to form dimers, that is, to pair and form surface > supercells (2x1, 2x2, 4x2, see the literature). > > If instead you want to converge exactly the system shown in your input > file, you should better use occupations=’smearing’ (otherwise the degauss > variable you next specify is useless!). Even though your surface is not > metallic, that can help to converge when there are near gap electronic > states, that “oscillate” in the scf convergence procedure. > > Moreover, the cutoff you use might be insufficient to get converged > results. > > Finally, to save computing time, the 4x4x4 k-point grid can be replaced > with 4x4x1, because sampling the Brillouin zone along the direction normal > to the surface is useless, if the periodic replica of the slab are > separated by vacuum space (z direction is in this case a “non-periodic” > direction, sampled with a periodic supercell). > > Giovanni > > > -- > > Giovanni Cantele, PhD > CNR-SPIN > c/o Dipartimento di Fisica > Universita' di Napoli "Federico II" > Complesso Universitario M. S. Angelo - Ed. 6 > Via Cintia, I-80126, Napoli, Italy > e-mail: [email protected] > Phone: +39 081 676910 > Skype contact: giocan74 > > ResearcherID: http://www.researcherid.com/rid/A-1951-2009 > Web page: http://people.na.infn.it/~cantele > > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum
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