'mode effective charge' in anaddb post-processing routine

Dear Abinit users,

What is the unit of the ‘mode effective charge’ in the output of the anaddb postprocessing file? The mode effective charge tensor is a number_of_modes tensor x 3 tensor. In comparison, the Born effective charge tensor is a number_of_atoms x 3 x 3 tensor.

I am interested in the mode polarity tensor (also a number_of_modes x 3 tensor), which is defined as the matrix product between the Born effective charges and the eigendisplacements (see Eq 41 in https://journals.aps.org/prb/pdf/10.1103/PhysRevB.71.125107):
p_{m,\gamma} = \sum_{\kappa, \beta} Z_{\kappa, \gamma \beta} u_m(\kappa, \beta)
, and I would like to understand what is the mode effective charge tensor in relation to p_{m,\gamma} .

Moreover, in the future, where can I easily find the units of the outputs and variables in Abinit?

Many thanks,
Virginie de Mestral
PhD student at ETHZ

Hi Virginie,

You can find the definition of the mode effective charge vector in Eq. 53 in https://journals.aps.org/prb/pdf/10.1103/PhysRevB.55.10355; it has units of charge.

All the best,


Hi Carl,

Thank you very much! This is exactly what I was looking for.