[Wien] Chemical Potential Boltztrap

[Gavin Abo]

I'm NOT an expert on BoltzTraP, but I try to answer your questions below.

> I just started to use the Boltztrap program. I have read a lot of papers using this program but I still have some questions related with the input and output files.
>
> Firstly: In most of the published articles they represent the seebeck coefficient as a function of the chemical potential. Usually in the x-axis they have zero value for the chemical potential; for example the case of Bi2Te3 in the main article. How do they get the zero value even though in the Bi2Te3.trace file there no zero value for the chemical potential. Do we need to substract a certain value from the column of the chemical potential?

I don't think so.  The values in case.trace should be partially 
controlled by the "Fermilevel (Ry), deltae, ecut, number of valence 
electrons" line in case.intrans [ 
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg08117.html 
].  I suspect deltae, which should control the increment of the x-axis 
values, was chosen such that 0 was included in the outputted chemical 
potential values.

> Secondly: in the case.intrance file there are two parameters that I can't understand the difference between them: ecut and efcut. As I understand that the chemical potential and the fermi level are synonym and they are equal to the fermi energy at 0 kelvin. So I think this parameters (ecut and efcut) should be synonym too.

In Table 1.1 of the BoltzTraP UserGuide there is:

ecut gives the range around efermi in which the bands are included

efcut. energy range of chemical potential around efermi that is used for 
integrals (Eqs.(p12-p15))

As it says, ecut is used to restrict what bands should be included in 
the calculation and efcut is used to specify the chemical energy range 
that should be used for the integration.

It looks like ecut is used in src/bandana.F90 and efcut in 
src/fermiintegrals.F90.

You'll likely see that ecut changes the output in BANDANA block in 
case.outputtrans, which should look something like:

==============  OUTPUT from BANDANA       ================
Fermi level changed to middle of gap. Ef = 0.05896
Egap:     0.122338 Energy range:    -0.141272 -     0.237481. Bands 
range:  101 -  140
VBM:    -0.002205 CBM:     0.120133 Efermi:     0.058964

==============  End BANDANA           ====================

On the other hand, efcut will likely change the chemical energy range 
that you see outputted in case.trace.

Say you have a total of 200 bands.  My understanding is ecut is like a 
coarse adjustment to include just the 101 - 140 bands as shown in "Bands 
range" above, while the efcut a finer adjustment to select say just the 
118 - 122 bands for the integration and to control the chemical energy 
range outputted (such as for plotting [ 
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10961.html 
, https://github.com/gsabo/BoltzTraP-Patches/tree/master/1.2.5 ]).

> Also in the case.intrance file at the we should insert the value of the fermi level. How can we get this value? Do we have to put the value of the Fermi energy that we have in case.scf file?

Yes, you should be able to grep for it [ 
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg11788.html 
, 
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg14185.html 
]; for example:

grep :FER case.scf*