Bug in the cell-optimization

xujroman leit... at matcalc.de
Mon Sep 7 10:03:28 UTC 2009


Dear Teo,

the following part of the input file ndescribes my unit cell:

   &CELL
       PERIODIC XYZ
         A 2.7 0.0 2.7
         B 0.0 2.7 2.7
         C 2.7 2.7 0.0
    &END CELL
    &TOPOLOGY
    &END TOPOLOGY
    &COORD
    Si                   0.00 0.00 0.00
    Si                   1.35 1.35 1.35
    &END COORD

Than CP2K performes a coordinat transformation:

 CELL_UC| Volume
[angstrom^3]:                                            39.366
 CELL_UC| Vector a [angstrom]     3.818     0.000     0.000    |a|
=       3.818
 CELL_UC| Vector b [angstrom]     1.909     3.307     0.000    |b|
=       3.818
 CELL_UC| Vector c [angstrom]     1.909     1.102     3.118    |c|
=       3.818
 CELL_UC| Angle (b,c), alpha
[degree]:                                    60.000
 CELL_UC| Angle (a,c), beta
[degree]:                                    60.000
 CELL_UC| Angle (a,b), gamma [degree]:
60.000

However the Si coordinates remain at the positions:

     1    1   Si   14    0.000000    0.000000    0.000000
4.00      28.0860
     2    1   Si   14    1.350000    1.350000    0.350000
4.00      28.0860

And this is of course not correct, because the periodic images are now
arranged in a wong way.

Regards,
Roman





On 7 Sep., 11:50, Teodoro Laino <teodor... at gmail.com> wrote:
> Dear Xujroman,
>
> what do you call "atomar basis". When the cell is rotated and aligned
> along the X,Y and Z axis the atomic coordinates are too...
> I don't see any evidence for the bug you're claiming to have found.
>
> Of course fee free to attach an input file that reproduces this error.
> Regards,
> Teo
>
> xujroman wrote:
> > Dear CP2K users,
>
> > I am performing a cell optimization using Cell_Opt and Geo_Opt for
> > bulk Si.
> > However, I recognized a bug during the setup of the unit cell.
>
> > If the starting cell vectors are given along arbitrary directions,
> > CP2K performes a coodinate transformation so that the first cell
> > vector (A) points along the x-axis. However, the atomar basis in the
> > unit cell is not transformed. That leads to a completely different
> > (wrong) atomic structure taking the periodic boundary conditions into
> > account.
>
> > The most simple way to avoid this bug, is to use cell vectors in such
> > a way that the A vector is parallel to the x-axis.


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