[Octopus-users] group symmetry problem in octopus

[David Strubbe]

Guoping,

Unlike GAUSSIAN, Octopus does not explicitly enforce symmetry, so the
symmetry will be broken to a certain extent by the real-space grid.
Decreasing the spacing to make a finer grid will help.  If you haven't found
this to be the case, probably the grid needs to be even finer.  I see from
your input file that you are using a spacing of 0.30 Å.  I think you need a
spacing of half that (0.15 Å) to get good results for C, as you can see from
the methane and benzene examples in the tutorial.  (Another issue could be
involved if the molecule's center of mass is not at the origin, in which
case the outer boundary of the spherical simulation box will break symmetry.
The solution then would be to center the molecule, or to increase the sphere
radius.)  Finally, it is possible that making the tolerance for SCF
convergence smaller would help, by setting, e.g. ConvRelDens = 1e-4.

David

On Tue, Jun 2, 2009 at 1:12 PM, Guo-ping Zhang <gpzhang at nano.indstate.edu>wrote:

> Dear octopus community,
>
> I just started to use octopus and do not have much experience, and I am
> interested in testing how good
> Octopus handles the symmetry. I tested
> both C60 and Benzene, and found they are not very good. For instance, for
> C60, I have energies like
>
> ....
>
>  108   --    -7.526996       2.000000      (8.3E-06)
>  109   --    -7.497639       2.000000      (8.1E-06)
>  110   --    -7.480991       2.000000      (8.0E-06)
>  111   --    -7.449556       2.000000      (7.6E-06)
>  112   --    -7.398673       2.000000      (7.9E-06)
>  113   --    -7.364355       2.000000      (7.3E-06)
>  114   --    -7.359087       2.000000      (5.6E-06)
>  115   --    -7.227304       2.000000      (8.2E-06)
>  116   --    -6.307225       2.000000      (5.5E-06)
>  117   --    -6.290637       2.000000      (7.4E-06)
>  118   --    -6.259217       2.000000      (6.1E-06)
>  119   --    -6.161393       2.000000      (2.5E-06)
>  120   --    -6.136155       2.000000      (2.8E-06)
>
>
> It seems the code breaks the symmetry already.
>
> Here is my input file for C60.
>
> Units = eV_angstrom
> CalculationMode = gs
> BoxShape = sphere
> radius = 12
> spacing = 0.30
> XYZCoordinates = "coords.xyz"
>
> EigenSolverInitTolerance = 1.0e-4
> EigenSolverFinalTolerance = 1.0e-7
> EigenSolverFinalToleranceIteration = 40
>
> ####ExtraStates = 2
> %Occupations
>
> 2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|
>
> 2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|
>
> 2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|2|
> %
>
> Note that I use the same geometry file on Gaussian, it does produce the
> symmetry correctly.
>
> I also notice that the mesh size does not help this either.
>
>
> I would appreciate it if you could give some advice on this.
>
> Best regards,
> Guoping
>
>
>
>
>
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>
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