[Phonopy-users] factor in phonon group velocity

[Liang C. <lia...@gm...>]

Dear Phono3py users,

I am using VASP and phono3py to determine the thermal conductivity of GaN.
I output the frequencies, group velocities, etc. I am confused about the
2pi factor for phonon group velocity.

In the manual, it is said the units of group velocity are The physical unit
is [image: \text{THz}\cdot\text{\AA}] (without [image: 2\pi]).  However, I
calculated the group velocity manually from d_omega/d_q where omega is
frequency*2pi, and q is calculated from reciprocal lattice vectors and
2pi/lattice_constant. The calculated value is same to the output directly
from phono3py. According to the manual, the calculated value should be
equal to the output times 2pi? Did I have any mistake here in my
calculation of group velocity? Thank you. I will appreciate any comment or
discussion.

Regards,


Liang Chen
Xi'an Jiaotong University
School of Energy and Power Engineering
28 Xianning Road, Xi'an, Shaanxi 710049, China