[QE-users] Regarding phonon calculations

[Mohad Abbasnejad]

Dear QE users,

Hello
I hope everybody is well.
I have two questions regarding phonon calculations.
1- I have calculated the frequency for special q point in my structure
shown as follow:

     Mode symmetry, C_3v (3m)   point group:

     freq (  1 -  2) =        -59.6  [cm-1]   --> E    L_3        I+R
     freq (  3 -  3) =        -48.4  [cm-1]   --> A_1  L_1        I+R
     freq (  4 -  5) =        162.4  [cm-1]   --> E    L_3        I+R
     freq (  6 -  6) =        227.4  [cm-1]   --> A_1  L_1        I+R
     freq (  7 -  7) =        250.8  [cm-1]   --> A_2  L_2
     freq (  8 -  8) =        295.5  [cm-1]   --> A_2  L_2
     freq (  9 - 10) =        299.4  [cm-1]   --> E    L_3        I+R
     freq ( 11 - 12) =        308.1  [cm-1]   --> E    L_3        I+R
     freq ( 13 - 14) =        382.0  [cm-1]   --> E    L_3        I+R
     freq ( 15 - 16) =        435.0  [cm-1]   --> E    L_3        I+R
     freq ( 17 - 17) =        456.0  [cm-1]   --> A_1  L_1        I+R
     freq ( 18 - 18) =        513.6  [cm-1]   --> A_2  L_2
     freq ( 19 - 20) =        521.9  [cm-1]   --> E    L_3        I+R
     freq ( 21 - 21) =        571.4  [cm-1]   --> A_1  L_1        I+R
     freq ( 22 - 23) =        578.0  [cm-1]   --> E    L_3        I+R
     freq ( 24 - 24) =        614.8  [cm-1]   --> A_1  L_1        I+R
     freq ( 25 - 25) =        620.5  [cm-1]   --> A_2  L_2
     freq ( 26 - 27) =        635.4  [cm-1]   --> E    L_3        I+R
     freq ( 28 - 29) =        651.0  [cm-1]   --> E    L_3        I+R
     freq ( 30 - 30) =        653.0  [cm-1]   --> A_2  L_2

I am wondering if somebody can tell me the meaning of I+R modes.
Does it mean Raman and infrared are active simultaneously for this mode?

2- I am wondering if increasing the threshold for self-consistency may
influence the frequencies significantly such that it causes the frequency
value from positive to negative. Is the default of the program reasonable?

Any help would be appreciated.

Bests
Mohaddeseh
-- 
---------------------------------------------------------
Mohaddeseh Abbasnejad,
Assistant Professor of Physics,
Faculty of Physics,
Shahid Bahonar University of Kerman,
Kerman, Iran
P.O. Box 76169-133
Tel: +98 34 31322199
Fax: +98 34 33257434
Cellphone: +98 917 731 7514
E-Mail:     mohaddeseh.abbasnejad at gmail.com
Website:  academicstaff.uk.ac.ir/moabbasnejad
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