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I need to determine which of two electrolyte is the best for a hydrogen fuel cell. As far as I understand, the first thing to do is to compute their ionic diffusion coefficient and to compare (the best electrolyte being the one with the highest ionic diffusion coefficient). I have never done an AIMD script. Would anyone know of existing scripts that I could adapt (even parts that I could try to complete)?

Any help appreciated, many thanks !

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2 Answers 2

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I see you used the the tag 'abinit' so I assume you want to do AIMD with abinit. Abinit's documentation is incredible and you should be able to make a lot of progress by looking there! See e.g. the topics page here and the tutorial on parallelism with MD which gives example input files and results here.

The 'ab-initio' part really just means that the forces are calculated with DFT vs classical MD where the forces use a classical force-field model. The MD-part (i.e. velocity integration) is very simple. Some codes do more sophisticated things than others, e.g. evolve the electronic coordinates in time using the Car-Parrinello method to avoid the SCF loop. Others extrapolate the density, etc. etc. Similarly, some codes implement more thermostats than others with more user control.

I think the MD code in abinit is less refined than other codes. If you want a more sophisticated MD code, you could try CP2K which also has a lot of examples. It is based on local-orbitals and is a little more geared towards molecules than solids, but I have used it to model crystals before. Quantum ESPRESSO is a good free software that uses plane waves. It has examples distributed with the source code and slides. Non-free codes like VASP have very sophisticated thermostats. See here. VASP also has example code in the tutorials.

Hopefully this helps get you started!

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    $\begingroup$ An excellent answer! $\endgroup$ Commented Mar 21 at 23:29
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Just adding to Tyler Sterling's excellent answer, there is also the CASTEP plane-wave DFT program, which is free for academic use (in fact any non-commercial use) and has quite a lot of MD functionality, including:

  • a range of ensembles (NVE, NVT, NPT, NPH)
  • several thermostats, including a fast equilibration thermostat (Andersen)
  • path-integral MD for quantum nuclear motion

See the documentation site MD pages for more details.

I've used CASTEP's MD quite a lot for a wide range of simulations, and I think it's quite easy to use (I'm a CASTEP developer though, so I'm not the best person to judge that!).

Edit: I should have added where to get the licence! It's here:

https://licences.stfc.ac.uk/product/castep

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    $\begingroup$ I have been meaning to try CASTEP for DFPT (I frequently use euphonic which interfaces with CASTEP), so it is good to know it is free to use! $\endgroup$ Commented Mar 22 at 13:32
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    $\begingroup$ @TylerSterling we'd be delighted if you gave it a try. We'd also welcome any feedback on usability, speed etc. those are my personal areas of interest, but it's always tricky to know what people would like. $\endgroup$ Commented Mar 23 at 0:14
  • $\begingroup$ @PhilHasnip It seems like we need to convince our advisors/faculty members to acquire the license. Is it possible for a grad student to obtain the license or some kind of trial license using the institutional email so that we can convince our superiors after giving it some trial? $\endgroup$ Commented Mar 23 at 1:54
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    $\begingroup$ @AbdulMuhaymin sorry for the delay. Unfortunately licences need to be signed by someone, even free licences, and legally most universities require this to be done by an employee - this isn't usually an academic though, it's usually someone in a "research grants and contracts" team. However, I think the commercial distribution does have a free 30-day trial option so perhaps you could try that? (I appreciate the irony here.) $\endgroup$ Commented Apr 11 at 13:10

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