[DFTB-Plus-User] electron phonon interaction and matrix derivative

[Haimen Mu]

Hi Gabriele,

I am also interested in the electron-phonon coupling related to dftb+. I read your python code ‘elcoupl.py’which gave me much inspiration,but I still have a small confusion. In your formulas ‘coupling = coupling - 0.5 * work2’ and ‘coupling = (coupling - 0.5 * work2) * prefactor’, there is a coefficient ‘0.5’that did not occour in some literatures. I saw formular in papers is like what Dirk Ziemann written in previous mail. That is ‘ gamma_ab^q   \approx  d H_ab / d_q  -  \sum_mn  d S_am / d_q * S^-1_mn * H_nb - \sum_mn  H_am * S^-1_mn * d S_nb / d_q ’. Would you explain the coefficient 0.5 here is for what?  

Looking forward to your reply.

Thank you .

Haimen Mu

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