[Pw_forum] k-points mismatch

Eyvaz Isaev eyvaz_isaev at yahoo.com
Sun Oct 5 13:46:05 CEST 2008 

Dear developers,

I have observed a mismatch between k-points generated 
by means of kpoints.x and phonons program, ph.x.

The problem is that first I did phonon calculations for a base centered orthorhombic cell (ibrav=9) using 4x2x2 mesh (10 q-points) and got an error message from q2r.x "q not allowed".
Well, something is wrong with the q-points. 
Then I tried to generate q-points using kpoints.x which stated that 4x2x2 mesh "has not the correct symmetry" and gave only 6 q-points.
OK, I used 4x3x3 to generate q-points and got 10 q-points without any message from kpoints.x.
But when I started phonons with 4x3x3 q-mesh, the ph.x program generated 14 q-points.

Can someone explain such kind discrepancy between two programs generating q-points? I used c/a=1.720447
and b/a=1.857204.

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


--- On Sun, 10/5/08, willy kohn <willykohn at gmail.com> wrote:

> From: willy kohn <willykohn at gmail.com>
> Subject: Re: [Pw_forum] Quick question on Hartwigsen-Goedeker-Hutter pseudopotential
> To: eyvaz_isaev at yahoo.com, "PWSCF Forum" <pw_forum at pwscf.org>
> Date: Sunday, October 5, 2008, 5:33 AM
> 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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> >
> >
> >
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