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Solve the Poisson equation with charge density data.

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Hi I'm currently trying to solve the Poisson equation in Comsol using the charge density data I obtained previously. I'm doing potential simulations in semiconductors and obtained the charge density I wanted. Now I'm trying to put that charge density data into the Poisson equation and solve for the potential. But in Comsol I can't find a way to give charge density data as an input to the Poisson equation. I can only give equations or single values. (through the Surface charge density, Space charge density nodes)

Is there a way to make this work? Please let me know if it's possible.


2 Replies Last Post Apr 15, 2021, 2:07 a.m. EDT
Robert Koslover Certified Consultant

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Posted: 3 years ago Apr 11, 2021, 10:04 p.m. EDT
Updated: 3 years ago Apr 11, 2021, 10:19 p.m. EDT

You didn't say whether these are: (a) two completely separate Comsol models, or (b) one model, but with two independent but sequential sets of physics/computations, or (c) one model with two related and interdependent computations that you wish to solve self-consistently. These situations would generally be handled in different ways.
Anyway, I'll take a wild guess and assume your models are completely separate and independent of one another (aside from covering identical spatial regions, at least in regard to where the space charge is located), and are thus most likely prepared as two different .mph files. In that case, my approach would be to: (1) simply plot and export to a file, the computed charge density data (as data) that you mentioned from the first model, then (2) import the data from that file into the second model, as part of my definition of an interpolation function, with its "data source" as the file that was exported from the first model, then (3) under space charge density (such as in the electrostatics formulation), specify the charge density to be given by the interpolated function (e.g, int1(x,y) ). I've tested this in 2D and it works just fine. Just make sure the two geometric spaces match and you have a fine enough mesh, etc. Of course, if you are trying to do something totally different, then you may wish to add more explanation here and/or post your model to the forum. Good luck.

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Scientific Applications & Research Associates (SARA) Inc.
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You didn't say whether these are: (a) two completely separate Comsol models, or (b) one model, but with two *independent* but sequential sets of physics/computations, or (c) one model with two related and *interdependent* computations that you wish to solve self-consistently. These situations would generally be handled in different ways. Anyway, I'll take a wild guess and assume your models are completely separate and independent of one another (aside from covering identical spatial regions, at least in regard to where the space charge is located), and are thus most likely prepared as two different .mph files. In that case, my approach would be to: (1) simply plot and *export* to a file, the computed charge density data (as data) that you mentioned from the first model, then (2) *import* the data from that file into the second model, as part of my definition of an *interpolation function*, with its "data source" as the file that was exported from the first model, then (3) under space charge density (such as in the electrostatics formulation), specify the charge density to be given by the interpolated function (e.g, int1(x,y) ). I've tested this in 2D and it works just fine. Just make sure the two geometric spaces match and you have a fine enough mesh, etc. Of course, if you are trying to do something totally different, then you may wish to add more explanation here and/or post your model to the forum. Good luck.

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Posted: 3 years ago Apr 15, 2021, 2:07 a.m. EDT

I had no idea I could create an interpolation function with given data! Also your guess of the problem (doing the simulation in two separate files) was correct! Thank you for your help.

I had no idea I could create an interpolation function with given data! Also your guess of the problem (doing the simulation in two separate files) was correct! Thank you for your help.

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