Multiwfn is able to plot difference of spin density between multiple wavefunctions as curve map, plane map or isosurface map, I think this is what you need. For example, Section 4.5.5 of Multiwfn manual illustrated how to plot isosurface map of electron density difference, you just need to choose spin density instead of electron density when Multiwfn asks you to choose the function to be plotted, then finally you will obtain isosurface map of spin density difference.By the way, Multiwfn is able to perform any mathematical operation for any supported real space function between any systems, the result can be exported or visualized.
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