Visualizing the charge distribution in COMSOL

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Discussion Overview

The discussion revolves around the visualization of charge distributions in COMSOL, specifically focusing on representing both continuous and discrete charge distributions during postprocessing. Participants explore various methods and features available in the software for depicting charge densities and induced bound charges, as well as the implications of these visualizations for understanding and presentation purposes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants suggest making a surface plot of the space charge density (es.rhoq) to visualize continuous charge distributions.
  • There is a discussion about the absence of discrete charges in the equations being solved, with some participants noting that only charge density is represented.
  • Some participants express a desire to visualize discrete +/- charges, arguing that point charges may provide a more intuitive understanding than surface distributions.
  • Questions arise regarding the visualization of induced bound charges, with some participants clarifying that this refers to the polarization of a dielectric.
  • One participant raises the issue of whether the visualization is for personal understanding or for presenting ideas to others, suggesting that a simplified representation may not convey the quantitative situation effectively.
  • Another participant emphasizes the importance of interpreting results based on charge density or polarization rather than relying on simplified representations of charges.
  • There is a mention of the potential to plot the polarization of materials and the challenge of accurately representing discrete charges due to their vast numbers.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness and appropriateness of visualizing discrete charges versus continuous charge densities. While some advocate for the use of simplified representations for clarity, others argue for the importance of accurately interpreting charge distributions without oversimplification. The discussion remains unresolved regarding the best approach to visualization.

Contextual Notes

Participants note limitations in representing discrete charges due to the nature of the equations being solved, as well as the potential for confusion when using simplified symbols to represent complex charge distributions.

feynman1
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How to visualize charge distributions in COMSOL, like showing + or - charges on a surface or a bulk in postprocessing?
 
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Make a surface plot of the space charge density (es.rhoq).
 
DrClaude said:
Make a surface plot of the space charge density (es.rhoq).
Thanks. That's a continuous distribution. What if I want to show discrete +/- charges?
 
feynman1 said:
Thanks. That's a continuous distribution. What if I want to show discrete +/- charges?
There are no such things as discrete charges in the equations being solved, only a charge density.
 
DrClaude said:
There are no such things as discrete charges in the equations being solved, only a charge density.
Right. So I assume there's no such feature of visualizing as point charges. Point charges look more intuitive than surface distributions.
 
  • Skeptical
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Is there a feature of showing induced bound charges?
 
feynman1 said:
Is there a feature of showing induced bound charges?
I dint understand. Do you mean polarization of a dielectric?
 
DrClaude said:
I dint understand. Do you mean polarization of a dielectric?
Yes, showing bound charges of a dielectric, caused by polarization.
 
feynman1 said:
How to visualize charge distributions in COMSOL, like showing + or - charges on a surface or a bulk in postprocessing?
Is the purpose of this for your internal 'understanding' or is it for the purpose of presenting ideas to others? I could see that a graphic of +and - charges could be familiar for people who are not well informed on the topic but why, as you are clearly familiar, would you want to go for a dumbed-down presentation? Presenting charge density as areas with random + or - signs scattered around could actually end up in a mess of symbols - if you actually want a hint of the quantitative situation. Just try it yourself, putting signs on a diagram, by hand. Is the result satisfactory?
 
  • #10
sophiecentaur said:
Is the purpose of this for your internal 'understanding' or is it for the purpose of presenting ideas to others? I could see that a graphic of +and - charges could be familiar for people who are not well informed on the topic but why, as you are clearly familiar, would you want to go for a dumbed-down presentation? Presenting charge density as areas with random + or - signs scattered around could actually end up in a mess of symbols - if you actually want a hint of the quantitative situation. Just try it yourself, putting signs on a diagram, by hand. Is the result satisfactory?
Kind of both. Would be nicer to show them in the simulation directly, without myself plotting them.
 
  • #11
feynman1 said:
without myself plotting them.
Yes - of course. But you can see the result for yourself with just one example. Perhaps, rather than spending effort on producing an inferior display system, you could work on a way to explain what the available charge distribution display shows. It's clearly so much more informative that I'm sure you could convince even the most reactionary audience.
 
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  • #12
feynman1 said:
Yes, showing bound charges of a dielectric, caused by polarization.
You can plot the polarization of the material.

To add to what @sophiecentaur said, it would be could for you to learn to interpret the results by looking only at the charge density or the polarization. Using + and - charges may be good for pedagogical purposes (I do use that when I teach), but you'll go farther by being able to lose those training wheels!

Remember also that the actual discrete charges are electrons and ions. Any accurate representation of the charges would include so many of them as to lead back to what you see using a surface plot...
 
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  • #13
DrClaude said:
You can plot the polarization of the material.

To add to what @sophiecentaur said, it would be could for you to learn to interpret the results by looking only at the charge density or the polarization. Using + and - charges may be good for pedagogical purposes (I do use that when I teach), but you'll go farther by being able to lose those training wheels!

Remember also that the actual discrete charges are electrons and ions. Any accurate representation of the charges would include so many of them as to lead back to what you see using a surface plot...
yes, one can plot polarization. nice to plot a finite number of +- charges to represent a surface distribution, if possible.
 

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