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[James Raynolds <JRaynolds@uamail.albany.edu>]

Martin,

        Please note: be careful to make sure where the Fermi level is.  It
doesn't always correspond to E = 0.  Also remember that with a different
unit cell you will be working in a folded zone picture.  Treat it as a metal
and take note of the fermi level.

        I've done the same type of calculation that you are talking about
and there was no problem.

Jim Raynolds

-----Original Message-----
From: trm@hrz.tu-chemnitz.de [mailto:trm@hrz.tu-chemnitz.de]
Sent: Monday, May 12, 2003 10:27 AM
To: forum@abinit.org
Subject: [abinit-forum] silicon band structure


Hello Abinit user,

we calculated band structure of silicon in differnet ways:

1. calculation with primitive cell

   ..............
        acell   10.217 10.217 10.217
        rprim   0.0 0.5 0.5
                        0.5 0.0 0.5
                        0.5 0.5 0.0
        natom   2
        type    1 1
        xred
                0.0  0.0  0.0
                0.25 0.25 0.25
  ...................

 this input give a right result,

2. calculation with unit cell


  ...............
        acell   10.217 10.217 10.217

        angdeg  90
                90
                90
        natom   8
        type    1 1 1 1 1 1 1 1

        xcart
        0.0000  0.0000  0.0000
        5.1085  5.1085  0.0000
        5.1085  0.0000  5.1085
        0.0000  5.1085  5.1085
        2.5543  2.5543  2.5543
        7.6628  7.6628  2.5543
        7.6628  2.5543  7.6628
        2.5543  7.6628  7.6628
  .................
  this calculation give a different result (no bandgap and completely
different bands)

We used the same Pseudopotential, the same calculationparameters and the
same
way throug the brillouin zone.

Using xred instead of xcart gives a new but also wrong result, where the
cells should be the same in both cases.

By calculating Siliconoxid with xcart or xred we get the right
bandstructure.

This is very confusing, have anybody a hint or idea what could be wrong and
how we could get the right bandstructure for silicon using the unit cell?


Thanks a lot,

Martin Trentzsch

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