Hello Everyone,
After a phonon calculation at q point how could I obtain the vibration
direction of each atom from the phonon eigendisplacements?
i.e: I know the eigendisplacements of M point and H point.
M point
Eigendisplacements
(will be given, for each mode : in cartesian coordinates
for each atom the real part of the displacement vector,
then the imaginary part of the displacement vector)
Mode number 1 Energy -1.376462E-04
Attention : low frequency mode.
(Could be unstable or acoustic mode)
; 1 8.85077623E-04 -1.53299946E-03 0.00000000E+00
; 0.00000000E+00 0.00000000E+00 0.00000000E+00
; 2 8.85074741E-04 -1.53299468E-03 0.00000000E+00
; 0.00000000E+00 0.00000000E+00 0.00000000E+00
; 3 9.25741287E-04 -1.60343070E-03 0.00000000E+00
; 0.00000000E+00 0.00000000E+00 0.00000000E+00
; 4 9.25744259E-04 -1.60343595E-03 0.00000000E+00
; 0.00000000E+00 0.00000000E+00 0.00000000E+00
H point
Eigendisplacements
(will be given, for each mode : in cartesian coordinates
for each atom the real part of the displacement vector,
then the imaginary part of the displacement vector)
Mode number 1 Energy -1.712882E-04
Attention : low frequency mode.
(Could be unstable or acoustic mode)
; 1 4.95643631E-05 7.10123124E-04 -2.67003155E-04
; -7.10123281E-04 4.95640911E-05 9.69330867E-04
; 2 -3.57461204E-04 -9.84627462E-05 1.92564773E-03
; -9.84632730E-05 3.57461134E-04 1.34403819E-04
; 3 5.49285047E-05 7.86977730E-04 -2.83291654E-04
; -7.86977167E-04 5.49283645E-05 1.02846494E-03
; 4 -3.96147876E-04 -1.09119309E-04 2.04312204E-03
; -1.09119475E-04 3.96148148E-04 1.42603120E-04
How can i get the vibration direction of each atom from the
eigendisplacements.
1,2 is O
3,4 is Zn
thanks and regards,
bin chen
Hello Chen,
the vibrations of the atoms are given precisely by the eigendisplacements: these are in cartesian coordinates, in atomic units (bohr), and give the displacements of each atom (the 1,2,3,4 in the first column after the semicolon is the atom number). These vectors are complex in general for q/=0.
To get the actual displacement in direction alpha of atom kappa in a cell at lattice vector R, you need to take the real part of the eigendisplacements times the Bloch factor exp(i q.R) which gives an additional phase:
\delta x_{\kappa,R,\alpha} = (R+x_\kappa^{(0)})_\alpha + Re(eigendisplacement_{\kappa,\alpha} * exp(i q \cdot R) )
Matthieu