Are there any LAMMPS packages/computes that can calculate the dynamical structure factor? I'm asking
because I did a search the LAMMPS mailing list and documentation, and I can't find a definitive package/compute to calculate the structure factor. What I did find what was prescriptions to use the lammps trajectory files
to calculate the structure factor. Am I missing something?
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I don’t think there is a compute to directly determine the structure factor, probably because the structure factor cannot easily be determined during a run because it is not a local property, so it would need information about all particles everywhere, which does not work well with neighbor list cut-offs and such. I assume in practice people probably just calculate the radial distribution function during a run and then take the Fourier transform afterwards. There is a compute called xrd which calculates an x-ray diffraction pattern which internally uses some form of structure factor, you could take a look in the source to see what they do.
Moreover, the dynamic structure factor looks at autocorrelation in time as well g(r,\tau) -> S(k,\omega). There’s no such package available as far as I know. There likely should be! As it is useful in a number of fields and not easy/possible to compute naively (considering the distance between every point in space and time). Looks like folks have talked about it before on the list. https://lammps.sandia.gov/threads/msg41468.html