Dear Eyvaz: Thank you for your long reply. What you mentioned was correct. I didn't expect LDA PP's can gave me a good prediction to the band gap and in fact the band gap given by the PP is closer to the experimental data than other PP's. What I would like to know is what value for Ge is 'typical' or 'normal' for a LDA PP.
Best, Wei On Thu, Oct 2, 2008 at 7:10 PM, Eyvaz Isaev <eyvaz_isaev at yahoo.com> wrote: > Dear Willy, > > --- On Fri, 10/3/08, willy kohn <willykohn at gmail.com> wrote: > > > I was told that with a LDA PP, Ge has a vanishing > > or negative band gap at Gamma point. But with this PP, > it has a gap of > 0.50eV (using experimental lattice) or > > 0.80 eV (after relaxation). > > Please recall that we use the Density Functional Theory, that is the theory > of the ground state, and it is not obliged to give correct excitation > energies in semiconductors. Besides, we apply the Local Density > Approximation which underestimates the band gap, even gives negative band > gap in Ge. This is well known fact. The source of this fault is the use of > single-particle Shrodinger equation, but the use of the quasiparticle > equation with the self-energy operator is more correct. There are few > recipes how to deal with this equation. The so called GW method is among > them. > > Another point is proper account of exchange-correlation interactions. It is > well known that the use of the functionals like PBE0, B3LYP gives improved > results for insulating systems concerning their electronic structure. For > the reference please have a look at /examples-EXX (for Si). > > So, if the HGH pseudopotentials are used in the framework of the DFT-LDA, > unlikely they can give correct band gap due to the fault of the underlying > method. > Even all-electron methods within the LDA fail to predict the band gap (as > example see PHYSICAL REVIEW B 67, 155208 2003). > > Bests, > Eyvaz. > > ------------------------------------------------------------------- > Prof. Eyvaz Isaev, > Theoretical Physics Department, Moscow State Institute of Steel & Alloys, > Russia, > Department of Physics, Chemistry, and Biology (IFM), Linkoping University, > Sweden > Condensed Matter Theory Group, Uppsala University, Sweden > Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com > > > > > > > > I'm not sure what I > > knew is correct, and that is the reason I wanted another PP > > to verify. > > > > Best, > > > > Wei > > > > > > > > On Thu, Oct 2, 2008 at 2:12 PM, Axel Kohlmeyer > > <akohlmey at cmm.chem.upenn.edu>wrote: > > > > > On Thu, 2 Oct 2008, willy kohn wrote: > > > > > > WK> Hi, Axel: > > > WK> > > > WK> Thanks a lot for your quick answer. I need to > > do some calculations on > > > some > > > WK> compound semiconductors of Ge. But the PP > > (Ge.pz-bhs.UPF) provided in > > > the > > > WK> PWSCF website yeided some results that I > > don't understand. So I would > > > like > > > > > > perhaps it would be useful to explain in more detail > > what > > > is confusing you and what calculation you did with > > what input. > > > perhaps some people here can comment on it. it is > > always easy > > > to blame the pseudopotential (sometimes rightfully > > so), but > > > more often than not, the real cause is in not doing a > > calculation > > > correctly, or not using a pseudopotential correct. > > > > > > WK> to use some other PP's to check if I did > > the calculation correctly. Any > > > WK> suggestions? > > > > > > i have a set of Ge pseudopotentials generated from > > parameters > > > for a norm-conserving troullier-martins potential that > > is in > > > the extended CPMD psp library. they have seen only > > very minimal > > > transferability testing (using an atomic code in > > bessel basis), > > > but so far seem to be ok, except for the OLYP one > > which has a > > > ghost in the s-channel. > > > > > > i can send them to you in a private mail, if you are > > interested. > > > no guarantees etc... > > > > > > cheers, > > > axel. > > > > > > WK> > > > WK> Best, > > > WK> > > > WK> Wei > > > WK> > > > WK> On Thu, Oct 2, 2008 at 11:54 AM, Axel Kohlmeyer > > < > > > akohlmey at cmm.chem.upenn.edu > > > WK> > wrote: > > > WK> > > > WK> > On Thu, 2 Oct 2008, willy kohn wrote: > > > WK> > > > > WK> > WK> Dear PWSCF users: > > > WK> > WK> > > > WK> > WK> I have a quick question about using > > > WK> > WK> Hartwigsen-Goedeker-Hutter< > > > WK> > > > > > > > http://cvs.berlios.de/cgi-bin/viewcvs.cgi/cp2k/potentials/Goedecker/abinit/pade > > > WK> > >pseudopotential > > > WK> > WK> with PWSCF. Is there any converter > > to transfer the HGH pp > > > WK> > WK> format to UPF used in PWSCF? > > > WK> > > > > WK> > none that i am aware of. > > > WK> > > > > WK> > the GTH pseudopotentials are analytical in > > real and reciprocal > > > WK> > space and to incorporate them properly, > > one would have to do a > > > WK> > lot of programming. in the CPMD code (from > > http://www.cpmd.org) > > > WK> > they are treated as a special case, > > similar to ultra-soft psps. > > > WK> > > > > WK> > is there any particularly reason you'd > > need any of those? > > > WK> > > > > WK> > cheers, > > > WK> > axel. > > > WK> > > > > WK> > > > > WK> > WK> > > > WK> > WK> Best, > > > WK> > WK> > > > WK> > WK> Wei > > > WK> > WK> > > > WK> > WK> Georgia Tech > > > WK> > WK> > > > WK> > > > > WK> > -- > > > WK> > > > > > > ======================================================================= > > > WK> > Axel Kohlmeyer > > akohlmey at cmm.chem.upenn.edu > > > http://www.cmm.upenn.edu > > > WK> > Center for Molecular Modeling -- > > University of Pennsylvania > > > WK> > Department of Chemistry, 231 S.34th > > Street, Philadelphia, PA > > > 19104-6323 > > > WK> > tel: 1-215-898-1582, fax: 1-215-573-6233, > > office-tel: > > > 1-215-898-5425 > > > WK> > > > > > > ======================================================================= > > > WK> > If you make something idiot-proof, the > > universe creates a better > > > idiot. > > > WK> > > > > WK> > > > > > > -- > > > > > ======================================================================= > > > Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu > > http://www.cmm.upenn.edu > > > Center for Molecular Modeling -- University of > > Pennsylvania > > > Department of Chemistry, 231 S.34th Street, > > Philadelphia, PA 19104-6323 > > > tel: 1-215-898-1582, fax: 1-215-573-6233, > > office-tel: 1-215-898-5425 > > > > > ======================================================================= > > > If you make something idiot-proof, the universe > > creates a better idiot. > > > > > _______________________________________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://www.democritos.it/mailman/listinfo/pw_forum > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... 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