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Quantum Dots and MATLAB

Posted Mar 19, 2010, 7:19 p.m. EDT 2 Replies

Dylan Gorman
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Hi folks,

I am trying to model a particular quantum dot in COMSOL. I am placing a number of electrodes on top of a substrate, specifying an electric potential on each of them, and solving Poisson's equation for the electric potential everywhere in the 3d model.

What I want to do is write a MATLAB routine that will vary the potential defined on one of the electrodes, and with each iteration I want to obtain the electric potential V(x,y,z), and feed this into an external density functional theory solver to calculate electron configurations.

The first problem I am running into that I cannot seem to find in the manual is that the solution, fem.sol.u, is a 1d array. I need somehow to obtain the real space representation V(x,y,z) from fem.sol.u.

I would appreciate any input that folks can offer on this (probably naive) question.

Thanks!
Dylan
2 Replies Last Post Jan 31, 2011, 1:02 a.m. EST
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Hello Dylan Gorman

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Waleed Shinwari
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Posted: 1 decade ago May 30, 2010, 9:39 p.m. EDT
This is not a naive question at all. I am facing the same problem with extracting data from COMSOL. I don't know the complete answer but I do know this: COMSOL, for some reason, plays around and shifts certain points in that fem.sol.u (perhaps to help for a more symmetric stiffness matrix). I think your best way of mapping the points back to the real space is either of the following:

1) why don't you just export the solution either in element node space, or in real symmetric cartesian space ? COMSOL can do that automatically and gives the output in a text file.

2) If not, you can get the mapping of the fem.sol.u points by calling the xmeshinfo function on the fem.xmesh (extended mesh). The output structure has a lot of info that will help you map the points back to their real space.

Sorry I realize my answer is vague but this is what I know at the moment
This is not a naive question at all. I am facing the same problem with extracting data from COMSOL. I don't know the complete answer but I do know this: COMSOL, for some reason, plays around and shifts certain points in that fem.sol.u (perhaps to help for a more symmetric stiffness matrix). I think your best way of mapping the points back to the real space is either of the following: 1) why don't you just export the solution either in element node space, or in real symmetric cartesian space ? COMSOL can do that automatically and gives the output in a text file. 2) If not, you can get the mapping of the fem.sol.u points by calling the xmeshinfo function on the fem.xmesh (extended mesh). The output structure has a lot of info that will help you map the points back to their real space. Sorry I realize my answer is vague but this is what I know at the moment
Aamir M
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Posted: 1 decade ago Jan 31, 2011, 1:02 a.m. EST
Hi,

Sorry I don't have any answer but some queries since I am doing a similar thing in comsol multiphysics.
I have got these GaAs/GaAs heterostructures on which I am applying certain gate voltage in some pattern. What I want to figure out is how do I model electrons rearranging. I don't know of any way in which I can put free electrons in the interface.

So its basically the same problem as you but I am doing on a GUI interface of COMSOL Multiphysics. Even if you could describe me the approach you are taking in MATLAB may be of help.

A response would be highly appreciated.

Hi, Sorry I don't have any answer but some queries since I am doing a similar thing in comsol multiphysics. I have got these GaAs/GaAs heterostructures on which I am applying certain gate voltage in some pattern. What I want to figure out is how do I model electrons rearranging. I don't know of any way in which I can put free electrons in the interface. So its basically the same problem as you but I am doing on a GUI interface of COMSOL Multiphysics. Even if you could describe me the approach you are taking in MATLAB may be of help. A response would be highly appreciated.

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