[Pw_forum] Quick question on Hartwigsen-Goedeker-Hutter pseudopotential

Sun Oct 5 03:33:41 CEST 2008

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.
> > >
> > _______________________________________________
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>
>
>
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