[QE-users] question about wave functions phonon code

[Jacopo Simoni]

(110) and (001), sorry.
These are both X points, equivalent under translation (the dynamical matrix
is the same also I checked in the code).

On Mon, 27 Sept 2021 at 12:25, Stefano Baroni <baroni at sissa.it> wrote:

> 100 is not equivalent to 110 in FCC … SB
>
> ___
> Stefano Baroni, Trieste -- http://stefano.baroni.me
>
> On 27 Sep 2021, at 19:55, Jacopo Simoni via users <
> users at lists.quantum-espresso.org> wrote:
>
> 
> Hi thanks for the reply. I need to compute a sort of finite temperature
> electron-phonon coupling, so I needed to go into the code and I wrote my
> own routine to do that, I am debugging the code and I noticed that the
> result at different but equivalent q points, let's say X=(1,0,0) and
> X=(1,1,0) in FCC are not the same as I should expect.
> Then I noticed that the wave function (evq) in reciprocal space differs
> (that is expected) but I do not understand  the relation between the two,
> that was why I was asking the previous question. In the meantime I found a
> mistake in the way I was computing the potential derivative, that is
> probably the main source of my problem. I was wondering also what does the
> routine symdyn_munu_new exactly do? Why does the dynamical matrix have to
> be symmetrized in the basis of the modes ?
>
> Thanks in advance,
> Jacopo Simoni, Lawrence Berkeley National Lab.
>
> On Mon, 27 Sept 2021 at 00:20, Lorenzo Paulatto <paulatz at gmail.com> wrote:
>
>> 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
>>>>
>>>> _______________________________________________
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>>
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