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Author Topic: Tr (k, e)/shift in Fermi level  (Read 10073 times)

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Offline Dipankar Saha

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Tr (k, e)/shift in Fermi level
« on: July 6, 2015, 11:51 »
For a "Spin: Unpolarized" calculation...while obtaining Tr (k, e) ..... I find it's only for "up-spin" component...!!! Whereas, all other calculations...e.g. n(r), del_n(r) etc. realted to that are done for "all spin"....!!! :o  What about the Seebeck co-eff. value...that we get from the "thermo-electric coefficients" plug-in ??  Is it considering the up-spin only??

Moreover, how do we select....del_Ef  (shift in Fermi level)....in the same plugin??

Regards_
Dipankar
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #1 on: July 7, 2015, 16:38 »
Quote from: Dipankar Saha on July  6, 2015, 11:51
What about the Seebeck co-eff. value...that we get from the "thermo-electric coefficients" plug-in ??  Is it considering the up-spin only??

Or, it's an Averagre ??!!  (Obviously, for Spin : UnPolarized  .... whether this is up-spin  or Average...should not matter.... )
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Offline Umberto Martinez

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Re: Tr (k, e)/shift in Fermi level
« Reply #2 on: July 8, 2015, 10:48 »
The thermoelectric coefficients plugins uses the transmission spectrum and for unpolarized calculations it uses spin sum (up+down) in the evaluation.

what do you mean with "how to select the energy shift"?
you can have a look at this tutorials:
http://quantumwise.com/publications/tutorials/item/515-isotope-impurity-effect-on-a-single-wall-carbon-nanotube
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #3 on: July 8, 2015, 12:36 »
Quote from: Umberto Martinez on July  8, 2015, 10:48
The thermoelectric coefficients plugins uses the transmission spectrum and for unpolarized calculations it uses spin sum (up+down) in the evaluation.

1) Meaning.....for unpolarized calculations  : even if the Tr(k, e ) is showing .... only the "up-spin" component as the active curve....; but still the calculation of "G(e)"  (as shown in the plugin) considers the sum.....!!!  :) 
Is it correct??
__________

2) In the same plugin .....while calculating the individual co-efficients....we have to set "T"...as well as  "del_Ef" .../ What this shift in Fermi level is relating to..??!!


Many thanks Umberto...!!!   :)
Regards_
Dipankar
« Last Edit: July 9, 2015, 19:21 by Dipankar Saha »
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #4 on: July 13, 2015, 15:22 »
Dr. Umberto Martinez,

Looking forward for your reply...  :) / Can you please tell me...how this "shift in Fermi level" is set ...??!!
 
[Some thing that is mentioned as...0.04 eV.... in the tutorial, you referred above.../ What "band edge" it corresponds to??!]

Regards_
Dipankar
« Last Edit: July 13, 2015, 15:24 by Dipankar Saha »
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Offline Umberto Martinez

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Re: Tr (k, e)/shift in Fermi level
« Reply #5 on: July 14, 2015, 15:04 »
Well you can calculate your coefficients at various energies.
The energy of the band edge is measured from the transmission spectrum
See also http://quantumwise.com/documents/tutorials/latest/Phonon/index.html/chap.thermoelectric.html#sect1.thermoelectric.analyze
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #6 on: July 14, 2015, 20:09 »
Thanks for your reply..... :)

Best_
Dipankar

« Last Edit: July 14, 2015, 20:51 by Dipankar Saha »
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #7 on: July 22, 2015, 22:30 »
Hello,
One more thing that I wanted to know is___

In a 2D plot.... say the y-axis  is showing Tr(k, e)...  while the x-axis  is given in terms of  Energy (eV)......

Is this energy scale itself represents (E-EF) ....??

Thanks & Regards_
Dipankar
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #8 on: July 23, 2015, 21:33 »
Quote from: Dipankar Saha on July 22, 2015, 22:30
Is this energy scale itself represents (E-EF) ....??
It will be of great help....if you can please reply... :)
_____
Besides, what happens exactly at  0 V bias (as well as, say there is no del_T) ....?? Does the chem. potential merge with the Fermi energy level?? But in ATK  EF is always represented as the energy zero..!!!

Thanks & Regards_
Dipankar
« Last Edit: July 23, 2015, 21:47 by Dipankar Saha »
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #9 on: July 23, 2015, 21:40 »
Moreover___
Is there any dipole formation at zero bias (something like, getting a local current??)  ??!!! :-\
« Last Edit: July 23, 2015, 21:47 by Dipankar Saha »
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Offline Jess Wellendorff

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Re: Tr (k, e)/shift in Fermi level
« Reply #10 on: July 27, 2015, 09:00 »
Yes, we will usually plot E-EF. This convention makes it easy to read the plot.
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #11 on: July 27, 2015, 09:38 »
Thank you Jess for the clarification...!!!  :)

Regards_
Dipankar
« Last Edit: August 8, 2015, 08:25 by Dipankar Saha »
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #12 on: August 8, 2015, 08:45 »
Using VNL-ATK 2015...I f we obtain  DDOS... for a spin unpolarized  calculation...it shows a projected 2D plot....where the down-spin component is exactly a mirror image of the up-spin one.
The problem is  that....... none of the objects of any specific *.nc file, obtained using 2015, is compatible with the ATK-VNL 2014.... Thereby,  I'm not being able to check....that if I render that DDOS object to the earlier version...
whether I will get the 'Sum' (i.e. , spin-up+spin-down = 2 x spin-up .... for this case) in DDOS v/s. Energy curve... or, it will be showing only the up-spin component??

Regards_
Dipankar
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Offline Jess Wellendorff

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Re: Tr (k, e)/shift in Fermi level
« Reply #13 on: August 10, 2015, 09:15 »
Great question. In ATK, an unpolarized DDOS consists of a spin-up and a spin-down component that are exactly identical. You can check this with "Text Representation". Both channels are plotted in the 2D Plot widget, but one of them can be "spin-flipped". Therefore, the total DDOS is 2xspin-up contribution = 2xspin-down contribution.
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Offline Dipankar Saha

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Re: Tr (k, e)/shift in Fermi level
« Reply #14 on: August 10, 2015, 12:11 »
Many thanks Jess... / That's exactly what I wanted to know..!!! :)

Regards_
Dipankar
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