structure factor compute?

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LAMMPS kspace_styles Ewald and PPPM both compute a structure factor (in parallel). The Ewald sum does this in the direct manner, and in fact does scale (non-optimally) as N^2. PPPM interpolates atoms to a mesh and uses FFTs, which gives it a N log(N) scaling. It probably wouldn’t be too hard to modify ewald.cpp or pppm.cpp to get what you want…

Stan

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This (the method Carsten Svaneborg described to calculate the structure factor) is exactly what the Ewald sum in LAMMPS does…

Stan

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Hi, Carsten. Sorry for the very belated reply. Thanks a lot for pointing this out! Unfortunately we require M^3 of order N, so I guess O(N^2) it is. But it is good to know, and if we ever can use a smaller M, we’ll put this info. to good use.

Thanks everyone for all the input!

Best,
Rob