[Pw_forum] Frozen phonon calculation using supercell in diamond structure

[Uri Argaman]

Dear QE users and developers
I'm trying to understand the shape of the normal modes in the diamond
structure and to calculate the frequency in the X symmetry point using
supercell (in addition to the regular DFPT calculation of QE). The atoms in
the unit cell in diamond structure are in (0,0,0) and (0.25,0.25,0.25). The
wave-vector in X is (2 pi/a,0,0). Therefore, these two atoms have a phase
difference of pi/2. Because of that I do not understand how to calculate
the frequency using supercell because there are no times in which the
kinetic energy are zero. Do I need to calculate the kinetic energy in these
kind of modes? can I do it classically?
Thank you in advance
Uri Argaman
Ben-Gurion University
Material Engineering Department
Israel
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