Hi, Ludwig
Raman modes should be calculate in primitive unit cell so you get the
correct number of phonon modes. In silicon you get six modes -- triply
degenerate Raman mode and three acoustic modes.
Sincerely yours,
M.V.Kondrin
On Nov 12 2023, [email protected] wrote:
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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