[Wien] MAE calculation-lack of the same symmetry like crystal structure.

[Peter Blaha]

Hi,

I can see from your table that the differences get smaller with 
increasing k-mesh.

I suspect that the shifting of the k-mesh may cause the problem (and 
these problems get smaller when the k-mesh is increasing).

Please check with non-shifted (gamma centered) k-meshes.

Regards

On 11/21/2017 04:59 PM, Jin Cao wrote:
> Dear Prof. Peter Blaha and wien2k users,
>     excuse me for seed this message twice again because this problem is
> so important for me and I am very very very looking forward for your
> reply!!!
>
>     I try to calculate the MAE of  two-layer Co2FeAl film with total
> energy method as mentioned in several mailing-list article. After the
> nosoc scf caculation, I add the soc self-consistent procedure and
> calculate the total energy with the direction 100, 010, 110 and -110
> respectively shown as attached file.
>     two-layer Co2FeAl film has 90 degree rotational symmetry of the Z
> axis, so the calculated MAE of 110 and -110 must be  equal to each
> other, but my results shown that
>                                            1.  MAE of 100, -100, 010,
> 0-10 are always the same with each other under the same  k-points;
>                                            2.  MAE of 110 and -1-10
> are  are always the same with each other under the same  k-points;
>                                            3.  MAE of 1-10 and -110
> are  are always the same with each other under the same  k-points;
> * Main problem Here: *  _4__.  MAE between 110 and -110 are always
> different with each other under __the same  k-points__ ._
> I can not understand the causes of this MAE symmetry-breaking because
> the 110 and -110 direction has the same chemical surrounding.(check the
> structure file~), Has anyone came across this problem and reply to me to
> help me with this problem?
>
> *Details of My calculation:*
> (1)Remove the symmetry of my structure to P1(only keep one sympo. in the
> case.struct file).
>                      The sympo. is:
>                                               1      NUMBER OF SYMMETRY
> OPERATIONS
>                                            1 0 0 0.00000000
>                                            0 1 0 0.00000000
>                                            0 0 1 0.00000000
>                                                     1
> (2)  After the nosoc scf caculation,I use the script initso_lapw to do
> the soc initialization, for example, i.e. 110:
>                            1...... (For R-lattice in R
> coordinates)(default 0 0 1): 1 1 0
>                            2......N  no atom without soc
>                            3......Emax = 10 Ry
>                            4......No RLOS
>                            5......y (run symmetso)
>                            6......Do you want to use the new structure
> for SO calculations ? (y/N)   y
> Then I find the weight of every kpoint is 1 in the case.klist file which
> means we calculate all of the kpoints in the BZ.Then we _runsp_lapw -so
> _and compare the total energy difference between different main axis to
> cauculate the MAE!
>
>
> *My question is:*
> (1) Does anyone who knows the cause of non-equivalence of 110 and 1-10
> direction and tell me how to solve it please~ To be honest, I have
> calcalated fcc-Co with the same procedure and also find
> the  non-equivalence of 110 and 1-10 direction!!!
>
> (2)I have known that different method of throwing kpoints impact the MAE
> largely, and the symmetry of the system determine the way of throwing
> kpoints, so the symmetry may largely impact the final results, Prof.
> Peter Blaha has recomanded to reduce the symmetry, so I  choose P1
> symmetry to cauculate MAE, is it really suitable or we need choose
> special symmetry for MAE calculation?
>
> (3)We guess that maybe the un-converged total energy cause the energy
> difference under low density kpoints, so we increase the kpoints to a
> large density(12800 kpoints in the full BZ with P1 symmetry), but the
> difference is still exists, we have increased the kpoints further,but we
> doubt that is this guess logical?!!!
>
> Thank you in advance!
>
> regards,
>
> Jinn
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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