[Pw_forum] Formatting for the interatomic force constant

[Hongze Xia]

Dear QE users and Prof. Giannozzi,

I did some web search and found no information about the formatting for the interatomic force constant (FC) created by "q2r.x". Could someone shed some light on this? I attached a sample file for it. It is the FC for the zinc blende GaN from a "4*4*4" phonon calculation. I did understand the first FIVE lines, which contains information of lattice type and its  lattice constant, masses and positions of basis. However the rest of the file is unclear to me. As I read from Prof. Giannozzi's paper, the real space force constants are in fact the inverse FFT from the reciprocal ones.

C_{s,t}^{alpha,beta} (R) = 1/N_C sum {e^{iqR}*C_{s,t}^{alpha,beta}(q)}

I guess the massive matrices are arranged in some order according the indexes "s,t,alpha,beta" and even "q" grid.

Thank you so much.

Best Regards,
Hongze Xia
PhD candidate in Photovoltaics Engineering
University of New South Wales
Sydney 2052 Australia
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