[QE-users] question about wave functions phonon code

[Lorenzo Paulatto]

Hello Jacopo,
instead of answering your question, I may ask you what you actually want to
do, because chances are that your problem has already been met by others.

E.g. there are ways to eliminate this phase, or to neutralize it to compute
the derivative w.r.t. the wave vector. But more often, when you have an
observable quantity that comes from a sum over the k-points, the phases
will cancel out in the total, if done correctly. It is actually a good way
to check that your formulas are correct.

Hth

-- 
Lorenzo Paulatto

On Sat, Sep 25, 2021, 21:28 Jacopo Simoni via users <
users at lists.quantum-espresso.org> wrote:

> So this means the phase factor is of the form e^{iG(k)r} where G(k) is the
> translation vector in rec. space such that
> G(k)+q+k=q'+k' (inside the first Brillouin zone)
> the phase factor is therefore dependent on the k vector and in reciprocal
> space the wave functions of the two equivalent q points are shifted by the
> vector G(k) ?
> Is there a variable in the code corresponding to this vector G or to the
> phase factor itself ?
>
>
> On Sat, 25 Sept 2021 at 03:42, Paolo Giannozzi <p.giannozzi at gmail.com>
> wrote:
>
>> On Sat, Sep 25, 2021 at 2:00 AM Jacopo Simoni via users <
>> users at lists.quantum-espresso.org> wrote:
>>
>> This wave function appears different from the wave function at an
>>> equivalent q point, for instance if I look at evq at q=(0,0,1), this is
>>> different from evq at (1,1,0) that are equivalent by translation of a G
>>> vector (I am thinking here at a FCC periodic lattice). The two functions
>>> just differ by a phase factor or I am missing something ?
>>>
>>
>> They differ by a phase factor; moreover, in the presence of degenerate
>> eigenvalues, you have no guarantee that the eigenvectors in the degenerate
>> subspace are the same. Finally, the ordering of k+G components is not
>> necessarily the same in the two cases
>>
>> Paolo
>>
>> Thanks in advance,
>>> Jacopo Simoni, Lawrence Berkeley National Lab.
>>> _______________________________________________
>>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
>>> users mailing list users at lists.quantum-espresso.org
>>> https://lists.quantum-espresso.org/mailman/listinfo/users
>>
>>
>>
>> --
>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
>> Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
>> Phone +39-0432-558216, fax +39-0432-558222
>>
>> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
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