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Charge unit in espresso #3633

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dpo854 opened this issue Apr 5, 2020 · 4 comments · Fixed by #3673
Closed

Charge unit in espresso #3633

dpo854 opened this issue Apr 5, 2020 · 4 comments · Fixed by #3673
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@jngrad
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Espresso 4.1.3

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@dpo854
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dpo854 commented Apr 5, 2020 •
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While going through the page on electrostatics, I realized that the prefactor should be KTlB/(eo**2) instead of kTlB as suggested by the package. Most example programs have mentioned the prefactor to be 2 and the charges to be integers. How do these charges connect to the electronic charge?
@dpo854
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dpo854 commented Apr 6, 2020

I guess the prefactor definition is wrong on the documentation webpage in that it should be eo**2/(4piepsilon0epsilonr). This makes it equal to lBkBT and for temperature =1 (in hoomd units), the prefactor is 2 for a sigma value of 0.35 and a Bjerrum length of 0.7 nm, which is the case for water.

@jonaslandsgesell
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jonaslandsgesell commented Apr 6, 2020 •
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Indeed, the documentation under http://espressomd.org/html/doc/electrostatics.html is inconsistent. C should be equal to C=eo**2/(4piepsilon0epsilonr) in equation (1) and the equation before needs to be adapated (via using valencies z_i=q_i/e_0)

@dpo854 dpo854 closed this as completed Apr 10, 2020
@jngrad
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jngrad commented Apr 10, 2020

Should we fix this or not?

@ggjj11
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ggjj11 commented Apr 10, 2020 •
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Yes, for clarity this should be fixed.

@jngrad jngrad reopened this Apr 10, 2020
@jngrad jngrad added this to the Espresso 4.1.3 milestone Apr 10, 2020
@jngrad jngrad self-assigned this Apr 20, 2020
@jngrad jngrad mentioned this issue Apr 20, 2020
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@kodiakhq kodiakhq bot closed this as completed in #3673 Apr 20, 2020
kodiakhq bot added a commit that referenced this issue Apr 20, 2020
@kodiakhq
Update documentation and clarify ambiguities (#3673)
f49d3b1 
Description of changes:
- remove CUDA installation instructions on OSX (follow-up to #3652)
- update links to dockerfiles for non-Ubuntu OSes
- correct the Coulomb prefactor formula (fixes #3633)
- in electrostatics scripts, replace magic values by their full expressions
- document the difference between serial and parallel versions of `libhdf5-dev` (fixes #3656)
- improve documentation of the script that shows the effect of MPI and `node_grid` on domain decomposition (see mailing list email "dividing simulation box using MPI" from 2020-04-20)
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Update documentation and clarify ambiguities jngrad/espresso
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