<div dir="ltr">Dear Eyvaz:<div><br></div><div>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.</div>
<div><br></div><div>Best,</div><div><br></div><div>Wei <br><br><div class="gmail_quote">On Thu, Oct 2, 2008 at 7:10 PM, Eyvaz Isaev <span dir="ltr"><<a href="mailto:eyvaz_isaev@yahoo.com">eyvaz_isaev@yahoo.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">Dear Willy,<br>
<div class="Ih2E3d"><br>
--- On Fri, 10/3/08, willy kohn <<a href="mailto:willykohn@gmail.com">willykohn@gmail.com</a>> wrote:<br>
<br>
> I was told that with a LDA PP, Ge has a vanishing<br>
</div>> or negative band gap at Gamma point. But with this PP, > it has a gap of 0.50eV (using experimental lattice) or<br>
<div class="Ih2E3d">> 0.80 eV (after relaxation).<br>
<br>
</div>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.<br>
<br>
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).<br>
<br>
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.<br>
Even all-electron methods within the LDA fail to predict the band gap (as example see PHYSICAL REVIEW B 67, 155208 2003).<br>
<br>
Bests,<br>
Eyvaz.<br>
<br>
-------------------------------------------------------------------<br>
Prof. Eyvaz Isaev,<br>
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia,<br>
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden<br>
Condensed Matter Theory Group, Uppsala University, Sweden<br>
<a href="mailto:Eyvaz.Isaev@fysik.uu.se">Eyvaz.Isaev@fysik.uu.se</a>, <a href="mailto:isaev@ifm.liu.se">isaev@ifm.liu.se</a>, <a href="mailto:eyvaz_isaev@yahoo.com">eyvaz_isaev@yahoo.com</a><br>
<div><div></div><div class="Wj3C7c"><br>
<br>
<br>
<br>
<br>
<br>
> I'm not sure what I<br>
> knew is correct, and that is the reason I wanted another PP<br>
> to verify.<br>
><br>
> Best,<br>
><br>
> Wei<br>
><br>
><br>
><br>
> On Thu, Oct 2, 2008 at 2:12 PM, Axel Kohlmeyer<br>
> <<a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a>>wrote:<br>
><br>
> > On Thu, 2 Oct 2008, willy kohn wrote:<br>
> ><br>
> > WK> Hi, Axel:<br>
> > WK><br>
> > WK> Thanks a lot for your quick answer. I need to<br>
> do some calculations on<br>
> > some<br>
> > WK> compound semiconductors of Ge. But the PP<br>
> (Ge.pz-bhs.UPF) provided in<br>
> > the<br>
> > WK> PWSCF website yeided some results that I<br>
> don't understand. So I would<br>
> > like<br>
> ><br>
> > perhaps it would be useful to explain in more detail<br>
> what<br>
> > is confusing you and what calculation you did with<br>
> what input.<br>
> > perhaps some people here can comment on it. it is<br>
> always easy<br>
> > to blame the pseudopotential (sometimes rightfully<br>
> so), but<br>
> > more often than not, the real cause is in not doing a<br>
> calculation<br>
> > correctly, or not using a pseudopotential correct.<br>
> ><br>
> > WK> to use some other PP's to check if I did<br>
> the calculation correctly. Any<br>
> > WK> suggestions?<br>
> ><br>
> > i have a set of Ge pseudopotentials generated from<br>
> parameters<br>
> > for a norm-conserving troullier-martins potential that<br>
> is in<br>
> > the extended CPMD psp library. they have seen only<br>
> very minimal<br>
> > transferability testing (using an atomic code in<br>
> bessel basis),<br>
> > but so far seem to be ok, except for the OLYP one<br>
> which has a<br>
> > ghost in the s-channel.<br>
> ><br>
> > i can send them to you in a private mail, if you are<br>
> interested.<br>
> > no guarantees etc...<br>
> ><br>
> > cheers,<br>
> > axel.<br>
> ><br>
> > WK><br>
> > WK> Best,<br>
> > WK><br>
> > WK> Wei<br>
> > WK><br>
> > WK> On Thu, Oct 2, 2008 at 11:54 AM, Axel Kohlmeyer<br>
> <<br>
> > <a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a><br>
> > WK> > wrote:<br>
> > WK><br>
> > WK> > On Thu, 2 Oct 2008, willy kohn wrote:<br>
> > WK> ><br>
> > WK> > WK> Dear PWSCF users:<br>
> > WK> > WK><br>
> > WK> > WK> I have a quick question about using<br>
> > WK> > WK> Hartwigsen-Goedeker-Hutter<<br>
> > WK> ><br>
> ><br>
> <a href="http://cvs.berlios.de/cgi-bin/viewcvs.cgi/cp2k/potentials/Goedecker/abinit/pade" target="_blank">http://cvs.berlios.de/cgi-bin/viewcvs.cgi/cp2k/potentials/Goedecker/abinit/pade</a><br>
> > WK> > >pseudopotential<br>
> > WK> > WK> with PWSCF. Is there any converter<br>
> to transfer the HGH pp<br>
> > WK> > WK> format to UPF used in PWSCF?<br>
> > WK> ><br>
> > WK> > none that i am aware of.<br>
> > WK> ><br>
> > WK> > the GTH pseudopotentials are analytical in<br>
> real and reciprocal<br>
> > WK> > space and to incorporate them properly,<br>
> one would have to do a<br>
> > WK> > lot of programming. in the CPMD code (from<br>
> <a href="http://www.cpmd.org" target="_blank">http://www.cpmd.org</a>)<br>
> > WK> > they are treated as a special case,<br>
> similar to ultra-soft psps.<br>
> > WK> ><br>
> > WK> > is there any particularly reason you'd<br>
> need any of those?<br>
> > WK> ><br>
> > WK> > cheers,<br>
> > WK> > axel.<br>
> > WK> ><br>
> > WK> ><br>
> > WK> > WK><br>
> > WK> > WK> Best,<br>
> > WK> > WK><br>
> > WK> > WK> Wei<br>
> > WK> > WK><br>
> > WK> > WK> Georgia Tech<br>
> > WK> > WK><br>
> > WK> ><br>
> > WK> > --<br>
> > WK> ><br>
> ><br>
> =======================================================================<br>
> > WK> > Axel Kohlmeyer<br>
> <a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a><br>
> > <a href="http://www.cmm.upenn.edu" target="_blank">http://www.cmm.upenn.edu</a><br>
> > WK> > Center for Molecular Modeling --<br>
> University of Pennsylvania<br>
> > WK> > Department of Chemistry, 231 S.34th<br>
> Street, Philadelphia, PA<br>
> > 19104-6323<br>
> > WK> > tel: 1-215-898-1582, fax: 1-215-573-6233,<br>
> office-tel:<br>
> > 1-215-898-5425<br>
> > WK> ><br>
> ><br>
> =======================================================================<br>
> > WK> > If you make something idiot-proof, the<br>
> universe creates a better<br>
> > idiot.<br>
> > WK> ><br>
> > WK><br>
> ><br>
> > --<br>
> ><br>
> =======================================================================<br>
> > Axel Kohlmeyer <a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a><br>
> <a href="http://www.cmm.upenn.edu" target="_blank">http://www.cmm.upenn.edu</a><br>
> > Center for Molecular Modeling -- University of<br>
> Pennsylvania<br>
> > Department of Chemistry, 231 S.34th Street,<br>
> Philadelphia, PA 19104-6323<br>
> > tel: 1-215-898-1582, fax: 1-215-573-6233,<br>
> office-tel: 1-215-898-5425<br>
> ><br>
> =======================================================================<br>
> > If you make something idiot-proof, the universe<br>
> creates a better idiot.<br>
> ><br>
</div></div>> _______________________________________________<br>
> Pw_forum mailing list<br>
> <a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
> <a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
<br>
<br>
<br>
_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
<a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
</blockquote></div><br></div></div>