Dear users:
I am going to calculate Raman spectra for organic perovskite. (only at Gamma
point)My flow chart is like this： pw.x vc-relax(geometry optimization)→pw.x
scf→ph.x→dynmat.xIn Phonon Calculation for Raman Spectra , How to decide to use
how many unit cells?
I saw what in the tutorial, for silicon in primitive cell, Si only has 2 atoms
in a primitive cell, and the tutorial used 2 atoms (1 unit cell to
calculate)Ref:https://www.quantum-espresso.org/wp-content/uploads/2022/03/phonons_tutorial_shanghai1.pdf
However, according to the paper I read, the author used 4 unit cells to
calculate, is this going to make some difference? Is it ok to calculate Raman
spectra with on one unit cell?Difference I could imagine is that if I had 1unit
cell with 24 atoms,With 1 unit cell (24 atoms), I can get 72(3*24) modes at
Gamma point. With 2 unit cell (48 atoms), I can get 144(3*48) modes at Gamma
point.
With 4 unit cell (96 atoms), I can get 288(3*96) modes at Gamma point.
As the unit cell increased, I would get more modes at Gamma point.However, it
takes more time to do the calculation.I'm wondering what's the difference to do
phonon calculation to use different number of unit cells? And how to decide it?
Best Regards,HY Lu
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