Is there a way to make the LAMMPS SPIN library work with micro units? (Magnetic microparticles in water)

LAMMPS LAMMPS Beginners
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1

Hi all,

I have been learning LAMMPS recently with the aim of modelling a 2D layer magnetic microparticles (diameter around 3um) in a solvent (typically water). I anticipate using MPCD to simulate the solvent (i.e. fix srd) and aim to model the microparticles as WCA hard spheres with spins linked to their centres. These spins interact via the spin/dipole/cut potential.

My problem is with the units of the LAMMPS SPIN library. In order to use the SPIN library, I need to use metal units where the distance is parameterised in Angstroms. However, my system is at the micron scale. Defining a box of 10000x10000 Angstroms takes way too long to run (even defining the system takes >1000x longer) so I am looking for ways to get around this problem.

Ideally, I would be able to translate the LAMMPS SPIN library and use micro units as this would work nicely with my system’s characteristic length and timescales. However, this doesn’t seem to be possible from what I can see.

My question is: Is there a way to make the LAMMPS SPIN library work with micro units?

(If micro units is more difficult, I would also be happy with lj units)

Thanks for your help!

3

I don’t understand your reasoning here. It doesn’t matter what units you are using.
Whether you are measuring distances in micrometers or angstroms, the distance remains the same, only the numbers are sometimes more and sometimes less convenient. The physics remains the same.

4

Agreed, the physics definitely remains the same, I just need to be careful with defining the correct distances.

My concern was to do with runtimes but I think my comments were premature. Defining the 100um box does seem to run on my device, just a bit slower than in micro units. Hopefully it should work okay.

Thanks for the quick response!