spin-dependent Seeback coefficients

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Hi all,
      If I perform a spin-polarized calculation for a magnetic device, can I get the spin-dependent Seeback coefficients? It seems that ATK can only give the total Seeback coefficients through the 'Thermoelectronic Coefficients' plugin in VNL.
Thank you in advance.

[Jess Wellendorff]

You are right, VNL currently calculates the Seebeck coefficient from the total electronic transmission spectrum (the sum of spin-up and -down spectra). So no, you are currently not able to get spin-resolved Seebeck coefficients.

- Jess

[Anders Blom]

... in the plugin.

But you can of course always evaluate it yourself from the spin-dependent transmission spectrum.

[bubble]

... in the plugin.

But you can of course always evaluate it yourself from the spin-dependent transmission spectrum.

Thank you for your reply, Blom.
However, can you please say it more clearly? Where can i get and install the plugin. It seems that the plugin is not in the "Addon manager".
Thank you in advance.

[Anders Blom]

I assumed you were already familiar with our tutorial on computing the thermoelectric coefficients?
http://quantumwise.com/documents/tutorials/latest/Phonon/index.html/chap.thermoelectric.html

[bubble]

I assumed you were already familiar with our tutorial on computing the thermoelectric coefficients?
http://quantumwise.com/documents/tutorials/latest/Phonon/index.html/chap.thermoelectric.html

Yes. However, what i want to know is the "spin-dependent" Seeback coefficients.
How can i seperate the spin-up and -down transmission spetra in one file in VNL? So we can calculate the spin-dependent coeffients seperately. are there some plugins?
Thank you!

[Jess Wellendorff]

The attached script shows how one should be able to calculate the Seebeck coefficient for each spin channel. You'll need an nc-file containing the electronic TransmissionSpectrum. The script has been only moderately tested, but I think it should work.

[bubble]

The attached script shows how one should be able to calculate the Seebeck coefficient for each spin channel. You'll need an nc-file containing the electronic TransmissionSpectrum. The script has been only moderately tested, but I think it should work.

Thank you for your help, Jess.
I will test it. If I have questions, I will contact you.

[bubble]

Thank you for your help, Jess.
As an example, I performed a spin-polarized calculations on a carbon nanoribbons with LSDA (the obtained transsmission spetra are therefore symmetric about spin-up and -down components, and the spin seebeck coefficent (SSC) should be the same for both spins).
I tested the 'seebeck.py' file that you provide, and found two questions:
Q1. Indeed, the spin-up and spin-down SSC are the same. I also calculated the total seebeck coefficent through 'thermalelectric coefficent', however, I found that the three values, spin-up, spin-down and the total, are the same. i.e. S1=S2=S. I think S should be equal to S1+S2?
Q2. If I want to get the relationship about S1~T, S2~T (T is the absolute temperature), what shall I do? (I understand that the default temperature is the electron temperature of two electrodes, for example, both are 300 K. How to get S1 and S2 under other temperatures?)
Thank you in advance!

[Jess Wellendorff]

Q1) The Thermoelectric Coefficients plugin gives you the average Seebeck coefficient (averaged over both spin channels). You therefore have the relation S = (S1+S2)/2.
Q2) To get the temperature dependence, the VNL plugin offers you the option of setting the temperature (300 K is default). You can do the same with the script: 300 K is default, but you can set the temperature like this:
*******
from NL.CommonConcepts.PhysicalQuantity import Kelvin
T = 400*Kelvin
S = evaluateThermoelectricTransportCoefficients(transmission_spectrum, spin, temperature=T)
*******

[bubble]

Hi, Jess, thank you very much for your reply.
As a further estimation, I calculated a spin polarized model according to the tutorial (i.e. http://www.quantumwise.com/publications/tutorials/item/112-transmission-spectrum-of-a-spin-polarized-atomic-chain)
For the parallel case, the spin-polarized spetra were well re-produced.
However, when I caculated the spin-seeback coefficients and total seeback coefficients of the system at 300K, the results are:

*************
spin=1 : Seebeck coefficient=-1.530e-06 V/K
spin=2 : Seebeck coefficient=1.236e-03 V/K
*************
Peltier Coefficient   -0.0004587   V
Seebeck Coefficient   -1.529e-06   V/K
Thermal Conductance (electrons)   8.206e-10   W/K
Thermal Conductance (phonons)   -   W/K
Thermal Conductance (total)   -   W/K
ZT   -
*************
I have two questions:

Q1.  It seems that S2 is larger than S1 by about three orders of magnitude (absolute values). however, the total S is only closed to S1. According to your above reply, I think S=(S1+S2)/2=S2 rather than S1. Is the result right?

Q2. This question is another independent question.
       I further caculated the spin-polarized transsimisson spetra of the sytems at finite bias (Vb=0.2 V) . How to get the spin-polarized current?  Through the Tool-Custom Analyzer-IVcurve, it seems that only total current can be obtained, although the  transsimisson spetra are spin polarized .

**********The results from IV Curve Plugin*****************
+----------------------------------------------------------+
| Current Report                                           |
+----------------------------------------------------------+
| Applied bias        = -0.200 Volt                        |
| Bias window         = [0.000 Volt, 0.200 Volt]           |
| Bias window covered = 100.00 %                           |
| Calculated current  = -1.51330794906e-05 A               |
| Spin                = Sum                                |
+----------------------------------------------------------+

Data for interpolation
Voltage list (Volt)
[-0.2]
Current list (nano Ampere)
[-15133.07949056]
**********************************************

In addition, the nc files are large (20-30 MB), so I can not upload them. But the script is uploded. See next!
Thank you in advance!

[bubble]

Here is the script

[Jess Wellendorff]

Q1
OK, I agree that the script I made does not quite cut it.
So I had a closer look at the theory of calculating the Seebeck coefficient (http://arxiv.org/pdf/1107.5687.pdf, page 3, top part of left column), and realized I had made an error
This should be fixed in the attached script. My output from the carbon chain transmission spectrum is:
**********
spin=1 : Seebeck coefficient = -1.530e-06 V/K
spin=2 : Seebeck coefficient = +7.274e-10 V/K
      total Seebeck coefficient = -1.529e-06 V/K
**********
The sum of the two spin contributions ("total") now matches the VNL result from the Thermoelectric Coefficients plugin.

Q2
For the IV curve plotting, I recommend you use the "IV-Generator" and "IV-Plot..." plugins (available in the right-hand panel next to LabFloor) instead of the Custom Analyzers.
Recipe:

• Highlight all your transmission spectra and use the IV-Generator to generate a single iv_curve.nc file.
• That file contains the I(V) object, which you can plot using the IV-Plot plugin.
• You can select which spin channels to see in the IV-Plot (Sum, Up, Down).

Best,
Jess

[wot19920302]

dear Jess Wellendorff ：         I inspect the script you offered above and can't understand this block:    

Code

 t1 = transmission_spectrum.evaluate(spin=spin)
                 t1 = SplineInterpolation1D(E, t1)
                 t2 = transmission_spectrum.evaluate(spin=Spin.Up)+transmission_spectrum.evaluate(spin=Spin.Down)
                 t2 = SplineInterpolation1D(E, t2) 

          It seems that you think spin-resolved seebeck coefficient should be calculated by 1/eT*(K1/K0), where K1 contains single spin transmission spectrum and K0 contains the sum of transmission of spin.up and spin.down. But in this paper:  Spin-dependent Seebeck effects in graphene-based molecular junctions (PHYSICAL REVIEW B 93, 195426 (2016) ),K1 and K0 seems only contains one type spin(up or down), do I misunderstand the script you offered?                 Best

[Jess Wellendorff]

This is an interesting question, and we are looking into it.