[QE-users] Inquiry Regarding the atomic displacement in Phonon Calculation

[zhouchao]

Dear QE Community,

I hope this message finds you well. First and foremost, I want to express my gratitude for the assistance and guidance you have provided in the QE community, which has been immensely beneficial to me.

I have a long-standing question that I hope you can help me with. In phonon calculations, we obtain vibration frequencies and eigenvectors from the matdyn.out file. I am particularly interested in understanding how to interpret the vibration modes. For example, 

************************************************************************      freq (    1) =      -0.000001 [THz] =      -0.000020 [cm-1]  (  0.010966   0.000000    -0.007875   0.000000     0.408025   0.000000   )  (  0.010966   0.000000    -0.007875   0.000000     0.408025   0.000000   )  (  0.010966   0.000000    -0.007875   0.000000     0.408025   0.000000   )  (  0.010966   0.000000    -0.007875   0.000000     0.408025   0.000000   )  (  0.010966   0.000000    -0.007875   0.000000     0.408025   0.000000   )  (  0.010966   0.000000    -0.007875   0.000000     0.408025   0.000000   )




(0.010966, -0.007876, 0) represents the vibration displacement of the first atom or the normalized coordinates? Are the units in atomic units? For orthogonal cells, can these numbers be directly converted to atomic displacements, but how to convert for non-orthogonal cells? How should the imaginary part be understood? Thank you very much for your help.

zhouchao
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