example of projected transmission

Asked by john on 2017-05-18

I'm trying to calculate the molecular projected transmission from tbtrans. But I'm not quite understand the statement
'One important aspect of projection is that the self-energies that are to be projected must be fully located on the projection region.'

I think it needs to be more specific in details. It will be better if there are some examples on molecular orbital projected transmission so we can learn to follow.

It seems that I have to extend the 'molecule' to the whole device region (which includes some metal atoms on both sides) to fulfill this requirement. Except that, the code exit with message like
'Left.M.HOMO
Region (109): Orbitals
  [ 478 -- 586 ]
Region (162):
  [ 244 -- 405 ]
The scattering states are not fully encapsulated on a left projection. This is not allowed. '

Do the orbitals in region 1 have to cover the 162 orbitals in region 2? How does the code determine region 2?

 Thank you!

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2017-05-18
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2017-05-18
Nick Papior (nickpapior) said : #1

Yes, this feature of tbtrans is not thoroughly documented. It proves to be quite trouble-some to create easy understandable documentation of this.
Once you understand it I would be more than great full if you could help the documentation by clarifing any misunderstandings.

As for your problem you have to select a device region such that any couplings from the electrode only couples into the projection region. I.e. if you have a system:
   L-chain-projection-chain-R
and you wish to project the incoming scattering states from the left you can select the device region to be
  projection-chain

If you want to project incoming and outgoing states you _have_ to select a device to only be:
  projection

This is because tbtrans "down-folds" the self-energies using the recursive method. The projection only happens in the device region. Please see this article for reference on the tbtrans method regarding "down-folding" and other details:
https://doi.org/10.1016/j.cpc.2016.09.022

Basically the first region is the projection region orbitals and the second region is the electrodes down-folded orbitals in the device region. So once region 2 is fully encapsulated in region 1, it runs.

Can you help with this problem?

Provide an answer of your own, or ask john for more information if necessary.

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