> Is there any reason for the different sizes of the tag_array and the
> real_map? real_map.last() and tag_array.last() show different results.

That was exactly the problem. The real_map is padded because of FFT requirements. The tag_array is not.

.real_map_unpadded() will make a copy. There will be another copy to restore the padding in .structure_factors_from_map() call. The two copies can be avoided in C++, but it is to cumbersome from Python.

Ralf