Re: [Phonopy-users] Problem with setting nac_params with Phono3py API

[Atsushi T. <atz...@gm...>]

I don't see how you define the word "erroneous". You should discuss
your physics with your supervisors and colleagues before asking
questions in the phonopy mailing list.

Mesh sampling calculation in phonopy is assumed to be used for
calculating macroscopic properties. Therefore it doesn't accept
q_direction because it breaks symmetry. But if you understand it, you
can run mesh sampling calculation first, then you can replace the
first element (=gamma point) by the result given by the q-point
calculation result. This situation exists in phono3py, for example, to
compute imaginary part of self energy at q->0.

I can answer your technical questions one by one. But unless you
understand your question clearly physically, my answers can be sent to
a trash can, which means my effort to answer will be vain, I lose my
time for nothing. So I will not want to answer more.

Togo

On Fri, Apr 30, 2021 at 2:49 AM Thomas Harrelson <tha...@gm...> wrote:
>
> Are there examples of how the choice of NAC direction leads to erroneous results? I know that in the Gonze paper, the authors discussed how the LO eigenvector can change with the NAC term, which may depend on the q-direction. Also, when using the Phonopy API to get phonons in mesh-mode, e.g.
> phonopy = phonopy.load(vasp_inputs, nac_params)
> phonopy.run_mesh()
> automatically sets the nac_q_direction to None during the operation of the code. So, is the only way to get the phonons with LO-TO splitting from phonopy using the phonopy.run_qpoints() method?
>
> Thanks for all the help by the way!
>
> On Wed, Apr 28, 2021 at 8:14 PM Atsushi Togo <atz...@gm...> wrote:
>>
>> Hi,
>>
>> It's implied by the formula. There is no standard direction.
>>
>> Togo
>>
>> On Thu, Apr 29, 2021 at 11:42 AM Thomas Harrelson <tha...@gm...> wrote:
>> >
>> > I see, so by default, setting the nac_params does not turn on the non-analytical term correction when calculating the phonons in mesh mode? Is there a standard direction that is typically used, or does the direction change the convergence rates, and thus any direction can be used?
>> >
>> > On Tue, Apr 27, 2021 at 8:06 PM Atsushi Togo <atz...@gm...> wrote:
>> >>
>> >> Maybe also, https://github.com/phonopy/phono3py/blob/5c66ad0a47ec349aa117f3f75b841242c6171d58/phono3py/api_phono3py.py#L926
>> >>
>> >> Togo
>> >>
>> >> On Wed, Apr 28, 2021 at 12:04 PM Atsushi Togo <atz...@gm...> wrote:
>> >> >
>> >> > Hi,
>> >> >
>> >> > See https://phonopy.github.io/phono3py/command-options.html#q-direction-q-direction/
>> >> >
>> >> > Togo
>> >> >
>> >> > On Wed, Apr 28, 2021 at 11:44 AM Thomas Harrelson <tha...@gm...> wrote:
>> >> > >
>> >> > > I am attempting to use the Phono3py API to calculate the imaginary self energy, phonon frequency, and phonon eigenvector arrays for further analysis within a code. I'm using this for materials with optically active phonons, so the NAC terms need to be present. At the moment, I'm following the code in Si.py script in the examples folder:
>> >> > >
>> >> > > primitive = phono3py.get_phonon_primitive()
>> >> > > nac_params = parse_BORN(primitive, filename="BORN")
>> >> > > nac_params['factor'] = Hartree * Bohr
>> >> > > phono3py.set_phph_interaction(nac_params=nac_params)
>> >> > > data = phono3py.get_phonon_data()
>> >> > >
>> >> > > Since the set_phph_interaction is deprecated, I also tried:
>> >> > > phono3py.nac_params = nac_params
>> >> > > phono3py.init_phph_interaction()
>> >> > >
>> >> > > In both of the above cases, the program works for GaAs, but there is no apparent LO-TO splitting for the optical phonons at gamma (all optical frequencies are the same), indicating that no NAC method was used. The phono3py._interaction object has the nac_params correctly loaded within it. Also, it appears that phono3py._interaction._dm has all the nac_params as well. Then why is there no LO-TO splitting? Am I setting up the code incorrectly, or what am I missing?
>> >> > > _______________________________________________
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>> >> >
>> >> >
>> >> >
>> >> > --
>> >> > Atsushi Togo
>> >>
>> >>
>> >>
>> >> --
>> >> Atsushi Togo
>> >>
>> >>
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>> >
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>>
>>
>> --
>> Atsushi Togo
>>
>>
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-- 
Atsushi Togo