[Pw_forum] IR+Raman modes in phonon calculations

[Deepashri Saraf]

Dear Users,

I am trying to perform phonon calculations for BaTiO3. After performing the
the calculations at gamma point, with the help of 'ph.x' executable, I get
following results for phonon frequencies,

------------------------------------------------------------------
Mode symmetry, C_4v (4mm)  point group:

     freq (  1 -  2) =       -190.6  [cm-1]   --> E    G_5 D_5    I+R
     freq (  3 -  3) =        -45.6  [cm-1]   --> A_1  G_1 D_1    I+R
     freq (  4 -  5) =         26.2  [cm-1]   --> E    G_5 D_5    I+R
     freq (  6 -  6) =        115.4  [cm-1]   --> A_1  G_1 D_1    I+R
     freq (  7 -  8) =        146.5  [cm-1]   --> E    G_5 D_5    I+R
     freq (  9 -  9) =        245.7  [cm-1]   --> B_1  G_3 D_2    R
     freq ( 10 - 10) =        268.0  [cm-1]   --> A_1  G_1 D_1    I+R
     freq ( 11 - 12) =        277.1  [cm-1]   --> E    G_5 D_5    I+R
     freq ( 13 - 14) =        457.1  [cm-1]   --> E    G_5 D_5    I+R
     freq ( 15 - 15) =        496.7  [cm-1]   --> A_1  G_1 D_1    I+R
---------------------------------------------------------------------

I could not set lraman=.true. as I was using ultra-soft pseudopotentials.

Following were the results for the phonon frequencies upon the application
of asr=simple with 'dynmat.x' executable.

--------------------------------------------------------------------

     IR activities are in (D/A)^2/amu units

# mode   [cm-1]    [THz]      IR
    1   -189.03   -5.6670   78.9556
    2   -189.03   -5.6670   78.9556
    3      0.00    0.0000    0.0000
    4      0.00    0.0000    0.0000
    5      0.00    0.0000    0.0000
    6    129.14    3.8716    8.7326
    7    140.75    4.2197    0.7690
    8    140.75    4.2197    0.7690
    9    260.86    7.8203    0.0292
   10    260.86    7.8203    0.0292
   11    263.08    7.8868    0.0000
   12    273.06    8.1862   42.5449
   13    456.98   13.6999    2.7989
   14    456.98   13.6999    2.7989
   15    502.29   15.0582   12.3293

-----------------------------------------------------------------------

These results are only for IR-modes. So my questions are as follows,

1. Does the "I+R" tag at the end of the output file given by ph.x
calculations, specify that the modes are both IR as well as Raman active?

2. Which are the correct values of IR frequencies? Those given by ph.x
calculations or by dynmat.x calculations?

Thanks in advance.

Best,
DS.

-- 
Deepashri Saraf
PhD Student
Department of Physics, SPPU
Pune (India)
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