Author Topic: calculation of optical spectrum versus applied external field  (Read 99 times)

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Offline korand

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Hi there,

I want to calculate optical spectrum (permittivity) of stacks of graphene layers by changing the external field (EF). Like what we know as changing chemical potential by changing applied EF in articles. How it is possible?
In my calculation I use GGA.PBE function and bulk configuration as version 2016.4 supports Optical Spectrum in this configuration.
I have read topic https://forum.quantumatk.com/index.php?topic=4011.msg18304#msg18304 but the first included link doesn't work properly.
I will appreciate it if you answer my question.
« Last Edit: October 9, 2020, 22:33 by korand »

Offline korand

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I am looking forward to the hearing from you!

Offline mlee

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Offline korand

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Re: calculation of optical spectrum versus applied external field
« Reply #3 on: October 14, 2020, 22:13 »
See the below link:
https://docs.quantumatk.com/manual/Types/OpticalSpectrum/OpticalSpectrum.html

More QuantumATK documents are in https://docs.quantumatk.com/
Dear Mlee
thanks for your answer to this topic.
But still i didnt get an answer. I know how to work with optical spectrum section in ATK. Unlikely, this section is just available in bulk configuration.
Again I clarify my question. I want to change the fermi level (chemical potential) of graphene and this would be happen by change electrical potential, apply different voltage at both surfaces of the graphene layer. (like what you see in fig. 6 of this article https://link.springer.com/article/10.1007/s10762-012-9946-2)
in other words, i want to put graphene as channel in a FET and set drain and source to ground and sweep the gate voltage and calculate the permittivity.
thanks in advance

Offline Tue Gunst

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Re: calculation of optical spectrum versus applied external field
« Reply #4 on: October 15, 2020, 11:36 »
Hi,
There are two ways to change the fermi-level.
1) By doping:
You can model this by using the atomic compensation charge (instead of including explicit dopant atoms):
https://docs.quantumatk.com/manual/Types/AtomicCompensationCharge/AtomicCompensationCharge.html#atomiccompensationcharge-c

2) By a true gate electrode:
Adding a metallic region and an adding an explicit charge to the LCAO calculator. See this link:
https://docs.quantumatk.com/manual/technicalnotes/doping_methods/doping_methods.html#atomiccompensationcharges
At the same time you need to take case of the boundary conditions for the Poisson solver.
This is described here:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.046601

I would think that the procedure in point 1) is what you seek. Changing the fermi-level and calculating the optical spectrum at each level.
Exactly what fermi-level shift the charge corresponds to can be seen in the band structure.
Alternatively the DensityOfStates analysis object has a method to evaluate the carrier density.