[Q-e-developers] Integration of EPW into QE 5

[Paolo Giannozzi]

On Mon, Jun 29, 2015 at 8:34 PM, Samuel Poncé <samuel.pon at gmail.com> wrote:

1) replace only set_irr.f90 and random_matrix.f90 with the previous versions
> elphmat(:,:,:)**2  0.1192375
> elphmat(:,:,:)**2  0.9861288
> elphmat(:,:,:)**2  1.354492
> elphmat(:,:,:)**2  0.3075966
>
> We get the old behaviour. Therefore only changing those two routines
> solves it ... but:
>
> 2 ) remove the "arg = randy(0)" line
>
> elphmat(:,:,:)**2  0.1192376
> elphmat(:,:,:)**2  0.9861288
> elphmat(:,:,:)**2  1.419427
> elphmat(:,:,:)**2  0.2426619
>
> 3)in set_irr.f90
> arg = randy(987654321)
>
> elphmat(:,:,:)**2  0.1192376
> elphmat(:,:,:)**2  0.9861287
> elphmat(:,:,:)**2  1.522261
> elphmat(:,:,:)**2  0.1398291
>
> 4 ) in set_irr.f90
> call set_rndm_seed(1)
>

no: "call set_random_seed ()", a different one


> but keep randy in random_matrix.f90
>
> elphmat(:,:,:)**2  0.1192375
> elphmat(:,:,:)**2  0.9861287
> elphmat(:,:,:)**2  1.419427
> elphmat(:,:,:)**2  0.2426619
>

the same as "randy(0)", since this is (I think) the default behavior of
randy if a seed is not set.

>
> As you can see the last two elements only are affected. Actually the two
> first one corresponds to irreducible modes that are non-degenerate and the
> two last one are irreducible with two degenerate modes (the sum of the
> degenerate mode should be fine though...).
>

wait  a minute:  the sum of the degenerate mode looks fine to me
   1.354492+0.3075966=1.6620886
   1.419427+0.2426619=1.6620889
   1.522261+0.1398291=1.6620901
and what you found earlier:
   1.348592+0.3134982=1.6620902
Once again: are you really sure that EACH of the above terms should not
depend upon the specific irrep? degenerate irreps span a well-defined
subspace but the specific choice of irreps will have an unpredictable phase

Paolo

-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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