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Warning: too many iterations in bisection 
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Joined: Fri Jan 12, 2018 9:29 am
Posts: 4
University: shanghai University
Post Warning: too many iterations in bisection
Dear sponce,
I use qe-6.4.0 package and the corresponding program EPW v.5.1.0 to start my work for calculating mobility. After Having done unfolding part, I set “int_mob = .true. and carrier = .true.” in the epw.in file to get the mobility. However, I find when the value of the parameter “ncarrier” is large (for example ncarrier = 1E19), I will get an incorrect Fermi level, meanwhile giving the tips “Warning: too many iterations in bisection”. The specific output in epw.out is as follows,
[i]
Temperature 100.000 K
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Warning: too many iterations in bisection
Ef = 0.000000
Mobility VB Fermi level 0.000000 eV
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Warning: too many iterations in bisection
Ef = 0.000000
Mobility CB Fermi level 0.000000 eV
Temperature 200.000 K
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Warning: too many iterations in bisection
Ef = 0.000000
Mobility VB Fermi level 0.000000 eV
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Warning: too many iterations in bisection
Ef = 0.000000
Mobility CB Fermi level 0.000000 eV
Temperature 300.000 K
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Warning: too many iterations in bisection
Ef = 0.000000
Mobility VB Fermi level 0.000000 eV
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Warning: too many iterations in bisection
Ef = 0.000000
Mobility CB Fermi level 0.000000 eV
Temperature 400.000 K
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Mobility VB Fermi level 0.859148 eV
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Mobility CB Fermi level 0.903837 eV
Temperature 500.000 K
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Mobility VB Fermi level 0.879921 eV
Valence band maximum = 0.848679 eV
Conduction band minimum = 0.909894 eV
Mobility CB Fermi level 0.883654 Ev

And I also notice that the Fermi level will get correct when carrier density is low or at high temperature. Therefore, how can this warning be avoided?
Another question, I find the EPW code cannot handle 2D materials, then is it the right treatment that treating 2D material as a 3D material with large value in z direction, and the corresponding carrier density of 2D material become the value of z direction times the value of “ncarrier” in 3D material.
Looking forward to your reply.

Changdong Liu


Fri Oct 04, 2019 5:54 am
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