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Note that there is no 2022.12 version, as you wrote...
I have no problems running this in V-2023.12-SP1, it converged in about 8 minutes on my laptop.
I don't recall exactly when we added stress to the planewave model. We can try to run your script in the new version if you share it, but we can't support the old version.
Hm, so effectively just creating a dipole in the metal? Not quite the same thing... Note that there is also non-conservation of the number of electrons in the central region so the charging of the molecule occurs not just from the neighboring metal atoms, but indeed from the infinite reservoirs.
Maybe it would be more efficient to consider a SurfaceConfiguration instead, which is a one-probe device with only one metal electrode, and you can run the potential of the metal to induce charge transfer to/from the molecule?
The photon mediated transmission is not plotted in the gui but you can obtain the data from the object as you are suggesting.
energies = photocurrent.energies().inUnitsOf(eV)
transmission = photocurrent.photonMediatedTransmission(photon_mode=0)
and then plot these two variables with pylab or other prefered plotting tools (select wanted photon_mode index for which you want to plot the transmission).
Please see the object description here for further details:
https://docs.quantumatk.com/manual/Types/Photocurrent/Photocurrent.html#NL.Analysis.Photocurrent.Photocurrent
Convergence checks should be performed for the usual DFT settings.
When a good DFT simulation has been performed the kpoints and energies/energy_resolution used in the Photocurrent calculation should be checked.
A bias voltage is included in the usual way through the device calculator. Then one perform the calculation of the Photocurrent for each separate and converged device configuration at a given bias voltage.
The Photocurrent object has a query function "photocurrent.photonMediatedTransmission(photon_mode,...)" that can be used to obtain the transmissions as a function of energy for a selected photon energy index "photon_mode".
Please see the reference manual entry for Photocurrent for full description of the inputs to this query function:
https://docs.quantumwise.com/manual/Types/Photocurrent/Photocurrent.html#photocurrent-c
If you set the confinement start radius and the radial cutoff radius very close one another, and increase the confinement strength dramatic, you will effectively have
a Sankey Hard Well potential.
Width of transmission resonances related to the HOMO and LUMO energy levels of the molecule is a measure of the coupling. In the limit of fully-decoupled molecule, the width goes to zero, as well as the coupling. This must be seen in the Transmission Spectrum, which can be computed in both 2015 and 2018 versions. If you use some simple tight-binding model, you may then try fitting parameters of that model to ab initio data obtained from QuantumATK Transmission spectrum. As an example of how ab initio derived conductance calculations can be interpreted using a tight-binding model, see Phys. Rev. B 74, 165416 (2006). It shows how the charge transfer and the coupling may affect the electron transport through molecule-like junctions. I also note that there must be a plenty of this kind of empirical studies on molecular junctions in the literature.
It is hard to give any short answers to your questions. There is a vast literature on this topic. So, I would suggest you searching and reading books and papers to learn about it.
2015.1 version is too old, so it is missing many features we have now in the code. You may still try using electron density and electron difference density to quantify the charge redistribution upon sandwiching the molecule between the two electrodes, e.g., see how that is done for covered surfaces, Eq. (2) and (3) in Phys. Rev. B 79, 195425 (2009). For your information, there is no support for 2015 version any longer.
