[Pw_forum] Problem in understanding the Phonon vibrational modes at gamma point
barnali bhattacharya
tintinsonapakhi at gmail.com
Thu Oct 26 08:55:56 CEST 2017
Dear Quantum ESPRESSO users,
I am trying to calculate the phonon vibrational modes at gamma point of a
periodic system by using quantum espresso. I successfully obtained the Mode
symmetry, VIBRATIONAL MODES and irreducible representations (GIVEN BELOW).
..........................................................................................
Mode symmetry, C_2v (mm2) point group:
freq ( 1 - 1) = 3.8 [cm-1] --> A_1 D_1 S_1 I+R
freq ( 2 - 2) = 6.9 [cm-1] --> B_1 D_3 S_3 I+R
freq ( 3 - 3) = 10.7 [cm-1] --> B_2 D_4 S_4 I+R
freq ( 4 - 4) = 158.2 [cm-1] --> B_2 D_4 S_4 I+R
freq ( 5 - 5) = 183.6 [cm-1] --> A_2 D_2 S_2 R
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freq ( 34 - 34) = 2000.0 [cm-1] --> A_1 D_1 S_1 I+R
freq ( 35 - 35) = 2188.1 [cm-1] --> A_1 D_1 S_1 I+R
freq ( 36 - 36) = 2213.4 [cm-1] --> B_1 D_3 S_3 I+R
...............................................................................................................
>From the output, I have understood the following points-
The point group symmetry of my system is C2v (mm2) and the number of
symmetry elements is 4 (A_1, A_2, B_1, and B_2)
There are 36 irreducible representations of the phonon modes (3 acoustic
and 33 optical modes) and all the modes are non-degenerate.
Optical phonon modes at the Γ-point are given by 11 A_1 +7 B_2+4 A_2+11B_1,
But I did not understand the 2nd last and 3rd last columns (D_1 S_1).
Could you please help me to understand the term D_1, S_1, D_2
............D_4, S_4 ?
I really appreciate your help in advance.
Sincerely
Barnali Bhattacharya
Ph.D scholar, Assam University,
Silchar-788011
Assam, INDIA
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