[QE-users] smearing vs. tetrahedron - weird behavior

[Paolo Giannozzi]

Not sure what is happening and why: the tetrahedron method works well for
"true" metals, maybe it doesn't work well for a case like yours. Look at
one-electron energies in the two cases and in particular to the position of
the impurity level (if easy to localize) and to its occupancy: is there any
other obvious anomaly?

Paolo
Paolo

On Sun, Mar 24, 2019 at 9:21 AM Christoph Wolf <wolf.christoph at qns.science>
wrote:

> Dear all,
>
> I am facing something rather interesting. My system is an insulator
> supercell with a metallic impurity. I tried to converge the Fermi energy
> wrt. to k-points and smearing in particular for "low temperatures" (~20 K).
> I observed the following behavior for a chosen number of k-points (e.g. 6 6
> 6 0 0 0): with smaller smearing the fermi level approaches the same value
> as the fermi level using the tetrahedron method (i.e. the tet_opt method
> represents 0 Ry smearing).
>
> however I found that for higher values for the k-point grid this does not
> seem to always work. For example for a 25 grid the value for the fermi
> level differs by ~0.8 eV! Is there a reason for this behavior?
>
> #k-grid kpnts Ef: smear tet
> 8      35  9.004  8.994
> *25  455  8.974  8.201*
> 26  560  9.006 8.996
>
> Your help is very much appreciated!
>
> Best wishes,
> Chris
> --
> Postdoctoral Researcher
> Center for Quantum Nanoscience, Institute for Basic Science
> Ewha Womans University, Seoul, South Korea
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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