Sorry but for 1 more naive question, if I use 2 unit cell instead of
1 in DFPT, would it be expected to have difference between the two
cases ( only at Gamma point) ?
yes, it is different. Because you would get twice as many phonons, but
half of them would be periodic inside the supercell (and correspond to
Gamma) the other would not be (and correspond to a zone-border q-point).
hth
Best Regards,
HY Lu
在 2023年11月15日 星期三 下午03:56:04 [GMT+8]， Lorenzo
Paulatto<[email protected]> 寫道：
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On 15/11/2023 08:45, [email protected]
<mailto:[email protected]> wrote:
Hope this will give you an idea why such*symmetry reduced* supercell
calculation is being carried out.
The idea is "symmetry reduced".
I.e. DFPT allows you to simulate a monochromatic perturbation of any
periodicity with a unit cell, while frozen phonon can only simulate
perturbation which have the periodicity of the cell you are using. But
to break symmetry, you need a supercell.
kind regards
L
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--
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
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