[Pw_forum] Problem with Raman and Infrared Active Modes: SOLVED

[HASAN SAHIN]

Dear Users,

In my previous e-mails I was asking about the eigenmodes that are both
Raman and IR active. Now I think it is solved.

When I calculate eigenfrequencies at gamma point, I had noticed that all
the modes are both Raman and IR active as follows

     omega(  4 -  5)   =         102.9  [cm-1]   --> E    L_3          I+R
     omega(  6 -  7)   =         156.9  [cm-1]   --> E    L_3          I+R
     omega(  8 -  8)   =         402.0  [cm-1]   --> A_1  L_1        I+R
     omega(  9 - 10)  =         719.8  [cm-1]   --> E    L_3          I+R
     omega( 11 - 11) =         831.9  [cm-1]   --> A_1  L_1        I+R
     omega( 12 - 12) =       1042.2  [cm-1]   --> A_1  L_1        I+R


Therefore I have tried to improve my calculation by

-increasing number of kpoints in scf part
-increasing ecutwfc and ecutrho
-using different pseudopotentials
-setting crystal structure as perfectly symmetric

but none of these improvements could give reasonable result about Raman
activity.



However, problem was solved by taking the values of tr2_ph less than
1.0d-24.  In this case we see that the modes becomes only Raman (or only
IR) active as follows

     omega(  4 -  5)   =        104.8  [cm-1]   --> E_g  L_3          R
     omega(  6 -  7)   =        165.5  [cm-1]   --> E_u  L_3'         I
     omega(  8 -  8)   =        398.5  [cm-1]   --> A_1g L_1         R
     omega(  9 - 10)  =        715.3  [cm-1]   --> E_g  L_3          R
     omega( 11 - 11) =        827.6  [cm-1]   --> A_2u L_2'        I
     omega( 12 - 12) =       1042.5  [cm-1]   --> A_1g L_1        R

I also would like to thank Martin Andersson, Paolo Giannozzi, Stefano
Baroni, Andrea Dal Corso  very much for their valuable comments and
suggestions.



-- 

*SINCERELY

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  Hasan Sahin
  Bilkent University
  National Nanotechnology Research Center

  http://www.bilkent.edu.tr/~shasan/

  http://www.researcherid.com/rid/G-4747-2010

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