[Pw_forum] Questions on phonon calculation in Example02 and 06

[vtmtrinh at caltech.edu]

Dear PWSCF Users,

  Since I would like to compare the phonon calculations by using 2
different ways as explained in Example02 and Example06, I rerun the
whole calculation in Example06. Everything was fine. I then rerun the
calculation of one specific q-point (-0.25, 0.25, -0.25) from Example06,
but using the way shown in Example02, ie. performing scf, calculation at
Gamma, nscf at q, and phonon at q.  I compared the 2 results from the 2
methods, I saw that both ways gave the same phonon frequencies, but the
displacement vectors are totally are different. I thought both should
have yielded the same results. I apprciate if you could you help me to
explain this.

Below are the results:

Following Example06:

 q = (   -0.250000000   0.250000000  -0.250000000 )
 **************************************************************************
     omega( 1) =       1.765425 [THz] =      58.888627 [cm-1]
 ( -0.141032  0.460061  0.040238  0.471692  0.181270  0.011631 )
 ( -0.113839  0.478895  0.071975  0.478895  0.185814  0.000000 )
     omega( 2) =       1.765425 [THz] =      58.888627 [cm-1]
 (  0.253069  0.173719 -0.286906  0.139072 -0.539975 -0.034647 )
 (  0.269727  0.160766 -0.283781  0.160766 -0.553509  0.000000 )
     omega( 3) =       4.536195 [THz] =     151.312190 [cm-1]
 ( -0.204646 -0.290110  0.204646  0.290110 -0.204646 -0.290110 )
 ( -0.455290  0.000000  0.455290  0.000000 -0.455290  0.000000 )
     omega( 4) =      11.004563 [THz] =     367.075159 [cm-1]
 ( -0.081755 -0.466090  0.446212 -0.432214  0.527968  0.033877 )
 (  0.039228  0.161901 -0.147017  0.161901 -0.186245  0.000000 )
     omega( 5) =      11.004563 [THz] =     367.075159 [cm-1]
 ( -0.451526  0.406642  0.107022  0.442481  0.558547  0.035839 )
 (  0.149460 -0.153037 -0.047572 -0.153037 -0.197033  0.000000 )
     omega( 6) =      12.136012 [THz] =     404.816481 [cm-1]
 ( -0.320406 -0.454213  0.320406  0.454213 -0.320406 -0.454213 )
 (  0.156090  0.000000 -0.156090  0.000000  0.156090  0.000000 )
 **************************************************************************



Following Example02

q = (   -0.250000000   0.250000000  -0.250000000 )
 **************************************************************************
     omega(  1) =       1.765442 [THz] =      58.889209 [cm-1]
 (  0.318551  0.007983 -0.249525 -0.028467 -0.568077 -0.036450 )
 (  0.325719 -0.012716 -0.256595 -0.012716 -0.582315  0.000000 )
     omega(  2) =       1.765442 [THz] =      58.889209 [cm-1]
 ( -0.451869  0.141577 -0.493353  0.138915 -0.041485 -0.002662 )
 ( -0.452021  0.174129 -0.494545  0.174129 -0.042524  0.000000 )
     omega(  3) =       4.536219 [THz] =     151.312986 [cm-1]
 ( -0.204633 -0.290122  0.204633  0.290122 -0.204633 -0.290122 )
 ( -0.455289  0.000000  0.455289  0.000000 -0.455289  0.000000 )
     omega(  4) =      11.004565 [THz] =     367.075220 [cm-1]
 ( -0.184054  0.641087 -0.184054  0.641087  0.000000  0.000000 )
 (  0.050209 -0.229371  0.050209 -0.229371  0.000000  0.000000 )
     omega(  5) =      11.004565 [THz] =     367.075220 [cm-1]
 (  0.384293  0.024658 -0.384293 -0.024658 -0.768587 -0.049316 )
 ( -0.135563  0.000000  0.135563  0.000000  0.271126  0.000000 )
     omega(  6) =      12.136049 [THz] =     404.817695 [cm-1]
 ( -0.320383 -0.454229  0.320383  0.454229 -0.320383 -0.454229 )
 (  0.156091  0.000000 -0.156091  0.000000  0.156091  0.000000 )
 **************************************************************************


Best,

MyTrinh Vo