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

Hi,

My question is: Why do you expect such thing to be orthorombic ?
If I compute a.b/||a||/||b|| with the coordinates you give for your a
and b vectors I clearly don't get 0 !
-(0.5*4.827496)**2 + (0.929695*8.976202)**2. Is it possible that the
structure you have entered is not the one you wanted to use for your
calculation ?

About performing convergence test at gamma: Yes it is usually
possible. However if your system is small and metallic it is still
wichable to have a few more k-point even for convergence test.

About PPMfrq:
You can have a look at :
http://www.abinit.org/Infos_v5.5/input_variables/vargw.html#ppmfrq
If you are not familiar with the plasmon pole model a very short
explanation (yet quite clear can be found at
http://theory.polytechnique.fr/resint/gw/gwintro/gwtheory.htm

Endly I definitely recommend you to take the time to follow the GW
tutorial : http://www.abinit.org/Infos_v5.5/tutorial/lesson_gw1.html
It comes with lot of useful explanations.

NOTE: The link in Abinit web site is broken ...

regards

PMA

On Tue, Mar 25, 2008 at 1:52 AM, Sophie Green <us_sophie.green@yahoo.com> 
wrote:
> Hi,
> I am very appreciate with your reply. I don't know how to enlarge the
> presicion in input file to give the correct symmetry. I checked the input
> variables, and still no results.
> I want to do the convergence tests, and I choose one point Gamma as what was
> done in the Si calculations in the test. Whether this method (choosing one
> point) is feasible? Besides, what is the meaning of ppmfrq in the input
> file? How we choose this value corresponding with our case?
>
>
> The following is my input file.
> kptopt1  1            # Option for the automatic generation of k points,
> nkpt1    432
> ngkpt1   12 6 12
> nshiftk1 1
> shiftk1  0.5 0.5 0.5  # These shifts will be the same for all grids
> # Definition of the SCF procedure
> toldfe1  1.0d-6    # Will stop when this tolerance is achieved on total
> energy
> prtden1  1         # Print out density
>
> # Dataset2: calculation of kss file
> # Definition of k-points
> kptopt2  0              # K-points will be provided
> nkpt2    1              # Take only 1 k-point:
> kpt2     0.0  0.0  0.0  # the Gamma point
> istwfk2  1              # Option needed for special k-points like Gamma
> # Definition of the SCF procedure
> iscf2    -2             # Non self-consistent calculation
> getden2  -1             # Read previous density file
> tolwfr2  1.0d-10        # Still get it converged
> nband2   13
>
> # Definition of parameters for the calculation of the kss file
> nbandkss2 -1        # Number of bands in KSS file (the maximum possible)
> # Dataset3: Calculation of the screening (epsilon^-1 matrix)
> optdriver3  3
> getkss3     -1
> nband3      37
> ecutwfn3    3.6
> ecuteps3    6.0
> ppmfrq3    16.7 eV
>
> # Definition of the unit cell: fcc
> acell  4.827496 8.976202 5.427863        # This is equivalent to   10.217
> 10.217 10.217
> rprim   0.500000  0.929695  0.000000   # FCC primitive vectors (to be scaled
> by acell)
>        -0.500000  0.929695  0.000000
>         0.000000  0.000000  1.124364
>
> # Definition of the atom types
> ntypat  1         # There is only one type of atom
> znucl 1           # The keyword "znucl" refers to the atomic number of the
>                   # possible type(s) of atom. The pseudopotential(s)
>                   # mentioned in the "files" file must correspond
>                   # to the type(s) of atom. Here, the only type is Silicon.
>
> # Definition of the atoms
> natom 12           # There are two atoms
> typat  1 1 1 1 1 1 1 1 1 1 1 1        # They both are of type 1, that is,
> Silicon.
> xred              # Reduced coordinate of atoms
>      0.50359   0.50359   0.63530
>      0.63171   0.63171   0.95315
>      0.76831   0.76831   0.81692
>      0.99641   0.99641   0.13530
>      0.86829   0.86829   0.45315
>      0.73169   0.73169   0.31692
>      0.00359   0.00359   0.86470
>      0.13171   0.13171   0.54685
>      0.26831   0.26831   0.68308
>      0.49641   0.49641   0.36470
>      0.36829   0.36829   0.04685
>      0.23169   0.23169   0.18308
>
> # Definition of the planewave basis set (at convergence 16 Rydberg 8
> Hartree)
> ecut 8.0          # Maximal kinetic energy cut-off, in Hartree
>
> # Use only symmorphic operations
> symmorphi 0
>
> # Definition of the SCF procedure
> nstep   20        # Maximal number of SCF cycles
> diemac  12.0      # Although this is not mandatory, it is worth to
>                   # precondition the SCF cycle. The model dielectric
>                   # function used as the standard preconditioner
>                   # is described in the "dielng" input variable section.
>                   # Here, we follow the prescription for bulk silicon.
>
> timopt -1
> # This line added when defaults were changed (v5.3) to keep the previous,
> old behaviour
>   iscf 5
>
> There is no ERR or WARN message in the output file, except that the wrong
> space group (monoclinic).
>
> Thanks very much for your help.
>
> Best Wishes,
>
> Sophie
>
> Anglade Pierre-Matthieu <anglade@gmail.com> wrote:
>  Hi,
>
> Usually Abinit understand input structures correctly. If it tells you
> that your input is monoclinic, it is quite likely this is true and it
> may matter a lot for your calculation if it is supposed to be
> orthogonal. Sometimes this kind of errors results from lack of
> numerical precision in the input file. Don't forget to use fraction,
> sqrt ... wherever relevant . The best for other people to tell you
> what is going wrong is to post your input file at least. May be some
> part of your output would be usefull too.
>
> About GW calculation: For as much as I know you just have to give
> Abinit the coordinates of each k-point you want to include. For
> instance if you want to use standard monkhorst pack gris plus some
> k-point you can first generate the list of coordinates for the
> monkhorst pack and then use kptopt 0, nkpt and kpt to specify the
> point you are interested in.
>
> regards
>
> PMA
>
> On Sun, Mar 23, 2008 at 11:22 AM, Sophie Green
>  wrote:
> > I am a new user to Abinit. I looked through the tutorial. I want to
> > calculate band gap with GW. I gave the conventional unit cell parameters
> > (acell) and rprim, also the atomic positions. But the output file shows
> > that the space group is monoclinic (P2_1/c). But it should be
> > orthogonal (cmca). I don't know why the space group is wrong. Will this
> > cause
> > mistake in the following calculations?
> > Besides, If the point I want to calculate in GW is nonspecific point,
> > what should I do to conclude this point in KSS calculation?
> > If anyone has this experience, please instruct me. Thanks in advance.
> >
> >
> > ________________________________
> >
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> > now.
>
>
>
> --
> Pierre-Matthieu Anglade
>
>
>
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Pierre-Matthieu Anglade