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[trm@hrz.tu-chemnitz.de]

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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