<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
Dear Robert,
<div class="">Just a quick comment.</div>
<div class=""><br class="">
</div>
<div class="">Are you looking just at the maximum of the curve? Did you check at which chemical potential this value occurs?</div>
<div class="">If you move the chemical potential well inside the conduction or valence band, the material will behave as a metal.</div>
<div class="">But to do this, you need a *huge* doping.</div>
<div class=""><br class="">
</div>
<div class="">You should instead check in the band structure, e.g. for p-doping, where the top of the valence band is, and then integrate the valence DOS to find where the chemical potential will be (at a given temperature) for the value of the doping of interest.</div>
<div class=""><br class="">
</div>
<div class="">(Or, if you are interested in the non-doped material, you should still compute the position of the Fermi energy, at charge neutrality, at a given finite temperature, that will be very close to the gap).</div>
<div class=""><br class="">
</div>
<div class="">If you check the value of the expected doping when mu is 1eV into the valence band, which I let you do it as an exercise, you will get that you are removing almost 1 electron (or even more) per unit cell, which is not realistic (please compare
with typical doping of silicon).</div>
<div class=""><br class="">
</div>
<div class="">I hope these comments will help you.</div>
<div class=""><br class="">
</div>
<div class="">Best,</div>
<div class="">Giovanni</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
<div class="">
<div>-- <br class="">
Giovanni Pizzi<br class="">
Theory and Simulation of Materials and MARVEL, EPFL<br class="">
<a href="http://people.epfl.ch/giovanni.pizzi" class="">http://people.epfl.ch/giovanni.pizzi</a><br class="">
http://nccr-marvel.ch/en/people/profile/giovanni-pizzi</div>
</div>
<div><br class="">
<blockquote type="cite" class="">
<div class="">On 3 Sep 2020, at 19:12, Robert Benda <<a href="mailto:robert.benda@enpc.fr" class="">robert.benda@enpc.fr</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="">
<div style="font-family: arial, helvetica, sans-serif; font-size: 12pt;" class="">
<div class="">Dear all Wannier users,<br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">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.
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">I attached the results I obtained for a 10 fs relaxation time as '<em class="">boltz_relax_time</em>' Boltzwann parameter.
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">The order of magnitude of the largest conductivity component is <em class="">
10^5 to 10^7</em> 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).
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">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.<br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">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.<br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">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).<br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">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.<br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">Thank you very much for your help,<br data-mce-bogus="1" class="">
</div>
<div class="">Best regards,<br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class="">Robert BENDA<br data-mce-bogus="1" class="">
</div>
<div class="">PhD student, CERMICS (ENPC) and Ecole Polytechnique (FRANCE)<br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
<div class=""><br data-mce-bogus="1" class="">
</div>
</div>
</div>
<span id="cid:C9FD1585-FED5-4267-BF19-FFCE53A5E298@epfl.ch"><cnt_elcond.png></span><span id="cid:F6A2C64A-6A00-4467-AEC2-E9E851A42371@epfl.ch"><Si_elec_conductivity_BoltWann_tau_10_fs.png></span>_______________________________________________<br class="">
Wannier mailing list<br class="">
<a href="mailto:Wannier@lists.quantum-espresso.org" class="">Wannier@lists.quantum-espresso.org</a><br class="">
https://lists.quantum-espresso.org/mailman/listinfo/wannier<br class="">
</div>
</blockquote>
</div>
<br class="">
</div>
</body>
</html>