[Pw_forum] hexagonal symmetry

[Arles V. Gil Rebaza]

Dear José, the difference between "a" and "b" parameter is around of
0.0000000009 bohr, this values is not important. And your hexagonal
symetries does not changes.

Best

PhD. Arles V. Gil Rebaza
Instituto de Física La Plata
La Plata - Argentina


2014-08-16 22:13 GMT-03:00 José Gadelha da Silva Filho <
gadelha at fisica.ufc.br>:

> Dear QE users,
>
> I am working with a hexagonal symmetry crystal and I relaxed all internal
> coordinates and cell parameters with vc-relax-bfgs algorithm.
>
> I have some concern about my results. So, I would like some advice.
>
> My initial cell parameter are:
>
>
> 45.48740530000000000 0.00000000000000000 0.00000000000000000
> -22.74370265000000000 39.39324854203890000 0.00000000000000000
> 0.00000000000000000 0.00000000000000000 10.31035723491920000
>
> with vectores  'a'  and 'b', as:
>
> a = b = 45.48740530000000000
> c = 10.31035723491920000
>
> After optimization I got this value:
>
> 44.53851082397360000 0.00000000000000000 0.00000000000000000
> -22.26925541198680000 38.57148182127630000 0.00000000000000000
> 0.00000000000000000 0.00000000000000000 10.12292974744850000
>
> In my calculation all operations symmetry  are conserved. However if use
> the cell parameters as:
>
> a = 44,53851082397360000
> b = 44,53851082482830000
> c = 10,12292974744850000
>
> The 'a'  and 'b' parameter aren't exactly the same.
>
> I did a test, where I use
>
> ibrav = 4
> celldm(1)=  44.53851082397360000,
> celldm(3) = 0.227284872 ,
>
> The component forces of atoms become high than  (>10-3).
>
> To keep the component forces of atoms less than >10-3,  I have to use
> ibrav = 0 and specify the matriz of cell parameters.
>
> With this process, Can I still consider my cell as hexagonal symmetry?
>
> Cheers
>
> --
> José Gadelha da Silva Filho
>
> Aluno de Doutorado do Curso de Pós-Graduação em Física
> da Universidade Federal do Ceará.
>
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-- 
###--------->   Arles V.   <---------###
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