Dear Reader,
I am new to KWANT and trying to figure out if it is suitable for calculating 
transport properties of gate-defined quantum dots made out of nanowires, along 
the lines of the structure used in https://arxiv.org/abs/cond-mat/0609463. Now, 
I understand that the mailing list is not a place to ask people to do my work 
for me, and my question is also not for someone to do this. What I am looking 
for is some insights into if this is possible (and not all that difficult) with 
the package.

At first sight (and going through the tutorials as well as the APS March 
Meeting material) this does not seem straightforward; what I struggle with is 
how to define this type of dot in KWANT. Now, one way would of course be to 
built the entire 3D geometry of the system, but this will be computationally 
expensive, and probably also rather tricky to do in terms of defining 
everything, from the hexagonal wire itself to all of the gates and oxide layers 
and such. Some abstraction would be preferred, perhaps even reducing the 
dimensionality and making a 2D system, such as often done in the tutorial. Is 
this a good idea?

My problem is that if one does this, then I run into the problem of how to 
model the 'half wrap-around' type gates typically used in these devices. In the 
transport through barrier section of the APS March Meeting material there is a 
section on how to model realistic potentials, but this would not work all that 
well for these wrap around type gates.

On the other hand, in a way they are perhaps not so different from the QPC in 
that section. One could model the three gates as something like 
https://i.imgur.com/WZC983c.png as they do essentially form channels in the 
wire. Apart from if this sacrifices too much of the nanowire nature in favor of 
a 2DEG system, I do suppose such a system should in principle be able to be 
treated as a quantum dot.

I haven't been able to confirm this as I am not yet sure how one can apply a 
source-drain voltage in KWANT; I first thought that this would probably be 
related to the energy of the modes, but then again I have not been able to 
produce Coulomb diamonds in this way.

The question is getting rather lenghty, and also a bit unclear at this point. 
Perhaps I should finish up by stating it in a concise form; would you think 
that it is possible to simulate the transport of such a gate defined nanowire 
quantum dot device with KWANT, and if so, is the approach I am suggesting above 
a viable one, or would you go about it very differently?

Kind regards
Jonathan



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