Dear all Wannier users,
I am quite new to Wannier90 and I am mostly performing electrical conductivity
calculations using the BoltzWann module. I have followed the tutorial (example
16) on the computation of Boltzmann conductivity tensor for Silicon.
I attached the results I obtained for a 10 fs relaxation time as '
boltz_relax_time ' Boltzwann parameter.
The order of magnitude of the largest conductivity component is 10^5 to 10^7
S/m, if I was not mistaken in the previous calculations using Quantum Espresso
(I used the default parameters provided in the example16/ repository as input
filesfor SCF and NSCF calculations).
I am very surprised, as I was expecting something of order 10^{-3} S/m, for the
conductivity of Silicon, which is a semiconductor. Increasing more the
relaxation time to 100 fs roughly produces a tenfold increase, accordingly to
the scaling factor of the relaxation time, on the conductivity, which happens
to be even larger, or order 10^8 S/m ; and farther away from the experimental
conductivity.
In all cases, as far as I know, relaxation times in most solids
(metals/semiconductors) range from a few fs to about 1000 fs -- that high, at
low temperature and for some low dimensional materials-- and in this range I
cannot reproduce a conductivity of order 10^{-3}, about 10 orders of magnitude
smaller than what I found.
Also for a carbon nanotube (which I am interested in in the end, comparing the
BoltzWann room T conductivity for defected CNTs / CNTs with adsorbed ions, to
the conductivity of the perfect, pristine CNT) provided in example15, I obtain
the same order of magnitude for the Boltzmann conductivity of the (5,5)
metallic CNT of about 10^6 S/m.(while rather expecting from 0.5-5 * 10^{2}
S/m).
Most probably I am missing a very basis subtlety in the input parameters or the
code using, that prevents me from recovering the correct orders of magnitude.
That is why I kindly request your help.
Thank you very much for your help,
Best regards,
Robert BENDA
PhD student, CERMICS (ENPC) and Ecole Polytechnique (FRANCE)
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