Dear PatrizioGraziosi,

We typically write out the structure in a file struct.xsf. When you perform density plotting, you also obtain the charge density (and you can also get the potential) as an XSF file. These files can be read in by xcrysden.

We don't support the bxsf file format, but it might be that xsf can be converted to bxsf, maybe by xcrysden. Beyond the mentioned quantities we don't write out other quantities to an xsf-like format.

You mean, you want to use the self-consistent density from FLEUR and use it for a single-shot calculation to obtain some property with QE? That is not possible because of many reasons. First, on the technical side the storage of the density for the different codes uses different formats. Next, a density you obtain from and use in pseudopotential calculations, like in QE, differs strongly from an all-electron density, as you have with FLEUR. For example because of the presence or absence of core electrons in the calculations.

If you want to use multiple codes, common approaches might be to do a structural optimization with one code and another part of the calculation with another. For example, you might want to perform a structural optimization with QE and then investigate some magnetic property, for example some spin-spiral dispersion with FLEUR. Different codes have different feature sets and strengths. By combining them you could get the best of different worlds. Such approaches would use self-consistent densities for each code separately. You might also perform the same calculations with different codes, just to check the agreement of the results, maybe just for a subset of very important calculations.

With respect to an xsf->bxsf conversion, that was just a guess from me. If you can't find something like that, it probably doesn't exist. Maybe you can write a converter on your own. At least the xsf file format is rather simple. I don't know how the bxsf file format looks like.

In general: If we write out xsf density files for plotting, they are really just for plotting. They don't have the resolution in the vicinity of each atom, that would be needed to perform some serious calculation with it.