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["Anglade Pierre-Matthieu" <anglade@gmail.com>]

PS: Also you don't mention cell parameter: Are you using the
experimental one, that of your ref. article or the one that yield no
pressure with your calculation setting ? This may have a sensible
effect...

On 9/27/07, Anglade Pierre-Matthieu <anglade@gmail.com> wrote:
> Hi,
>
> Band structure depend on:
> -XC functional (with Abinit you set that with "ixc")
> - it can depend on pseudopotentials (yet it shall not if the
> pseudopotentials are corrects)
> -it depends on the quality of the convergence of your calculation.
>
> On this last point I have a few comments (may be because you have just
> omitted to tell us about those point in your mail; but it is worth
> checking if you haven't already done so).
> You may try:
> - to set a finer K-point mesh
> - to be sure that 50 Ha of cutof fis enough for the pseudopotentials
> you use (I would guess Cd pseudopotential to be quite hard)
> - to check the band convergency during your  SCF iterations:
>   a) Be sure that you include enough bands. In your case you let
> Abinit use the default. Although it should be enough in your case, you
> can try to add a few. The algorithm that check the convergence of the
> non self consistent iteration do not take care of the two last bands
> and maybe your conduction bands are not converged enough ?
>   b) Some systems converge badly. You may have to increase your
> convergence criterion in order to get small values (1e-4 or less; 1e-8
> is overkiling ) for both what Abinit calls Vres2 and residm. If one of
> them is big at the end of your SCF calculation it may be the source of
> your problem.
> - choose a different XC functional that gives results closer to litterature
> -Also it is important to be certain that the k-lines under examination
> are those that include the max and min of the valence and conduction
> bands.
>
> Hoping one of this comments helps.
>
> regards
>
> PMA
>
>
>
> On 9/26/07, Hua Bao <hbao@purdue.edu> wrote:
> > Dear Abinit-user,
> >
> > I am trying to do a CdTe band structure calculation using ABINIT. I
> > followed the literature Physica B 373 (2006) 124-130. They used "
> > first-principles pseudopotential method within the density functional
> > formalism and the local density approximation using the Coperley-
> > Alder functional for exchange-correlation energy, and standard norm-
> > conserving pseudopotential of Troullier-Martins in non-relativistic
> > form". Also, they use a mesh cutoff of 100 Ry and 108 k points. They
> > are using a different codes.
> >
> > Follow them, I calculated the band structure of CdTe with the similar
> > parameters. However, I got a huge underestimate of band gap. The
> > literature gives 1.88 eV, I got only 0.45 eV in the ABINIT
> > calculation, experimental result is 1.56 eV. I even tried GW method.
> > It still got 0.97 eV which is still much less than experimental
> > result (some others using GW got 1.88 eV).
> >
> > My question is how does this happen. Is band structure result codes-
> > dependent? Is there anyway to improve the result for band structure?
> >
> > BTW, I am using 48cd.pspnc and 52te.pspnc from the ABINIT website.
> > Here is the input file for band structure calculation.
> > #Data set
> > ndtset 2
> >
> > #Definition of the unit cell
> > acell  6.480 6.480 6.480  angstrom
> > rprim 0 .5 .5
> >        .5 0 .5
> >        .5 .5 0
> > #Definition of the atom types
> > ntypat 2
> > znucl 48 52
> >
> > #coordinates
> > xred 0 0 0
> >       0.25 0.25 0.25
> > #Definition of the atoms
> > natom 2
> > typat 1 2
> >
> > ecut 50.0         # Maximal kinetic energy cut-off, in Hartree
> > #Functional
> >
> >
> > #Data 1
> > #Definition of the k-point grid
> > ngkpt1 6 6 6
> > kptopt 1
> > prtden1 1
> > toldfe1 1.0d-6
> > nshiftk1 4
> > shiftk1  0.5 0.5 0.5  # These shifts will be the same for all grids
> >           0.5 0.0 0.0
> >           0.0 0.5 0.0
> >           0.0 0.0 0.5
> >
> > #Dataset 2
> > iscf2 -2
> > getden2 -1
> > kptopt2 -3
> > nband2  18
> > prtwf2 0
> > prteig2 1
> > ndivk2 20 20 20
> > kptbounds2      0.5  0.0  0.0 # L point
> >                  0.0  0.0  0.0 # Gamma point
> >                  0.0  0.5  0.5 # X point
> >                  1.0  1.0  1.0 # Gamma point in another cell
> > tolwfr2 1.0d-12
> > enunit2 1
> >
> > #Definition of the SCF procedure
> > nstep 100          # Maximal number of SCF cycles
> > ixc 2  (I also tried 1).
> >
> >
> >
> > Hua Bao
> > Graduate Research Assistant
> > School of Mechanical Engineering,
> > Purdue University
> > O: 765-494-6944
> >
> >
> >
> >
>
>
> --
> Pierre-Matthieu Anglade
>


-- 
Pierre-Matthieu Anglade