Dear yang,

Fleur can be used for this purpose, but more in the sense that the results from Fleur calculations can be used in a manual postprocessing step to calculate these parameters. How this is done in detail depends on your use case. The simplest approach is to perform calculations with different magnetic configurations and then set up a system of linear equations constructed from the different configurations, the total energies of these calculations, and the respective coupling constants. You then obtain the coupling constants by solving this system of linear equations.

For other cases a good starting point for the calculation of exchange coupling parameters is a set of calculations for different spin-spirals. Such an approach is suggested in this paper. Fleur explicitly supports such calculations in terms of the magnetic force theorem. The usage of this feature is sketched here.