Are the polar-phonon frequency and the longitudinal optical phonon the same thing?

AMSET
1

Dear Alex,
Are the polar-phonon frequency and the effective longitudinal optical phonon the same thing ?
If not , how to calculate the effective longitudinal optical phonon?
Best wishes,
zhenqing

2

Yes, the polar phonon frequency and the effective longitudinal optical phonon are the same thing. They are calculated using amset phonon-frequency.

1 Like
3

hello .alex
when i calculate phonon-frequency ,it always come out wrong,

My calculations are always at 0.85Thz，when i calculate Ga2O3, but this results is obviously wrong. and i estimated it should more than 10Thz.

and ,there is a strange phenomenon here.
when i use primitive cell(20atom)it is 0.84Thz.but when i use supercell(80atom).it is 12.48Thz
this is coufusing me .

this is mt input about phonon-frequency
image
image

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image365×749 14.3 KB

this is 20atom primitive cell
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image493×869 27.6 KB

this is 180 atom supercell

4

It seems like the highest frequency in your primitive unit cell calculation is 1.42 THz. So its not clear how amset would ever calculate a phonon frequency > 10 THz.

Can you:

  1. Make sure amset is the most recent version.
  2. Make sure your primitive cell calculation doesn’t have any errors.

Best,
Alex

5

thank you so much your reply.
but i also have a qurestion ,
for this material it"s pop_frequency always range from 8.44Thz to 11.60Thz.
but it’s 0.84Thz in the amset phonon-frequence. it make me confused .Can you answer this for me .

best wishes

6

Hi @LLei,

I’m afraid I don’t understand your question? Were you able to check your VASP calculation to ensure that the phonon frequencies were correct (i.e., they are giving frequencies in the correct range). Secondly, you should check you are using the latest amset version.

If you’re sure its an issue with amset you can upload the vasprun.xml and I will take a look.

Best,
Alex