  We extend the frozen density embedding theory to non-integer subsystems'
particles numbers. Different features of this formulation are discussed, with
special concern for approximate embedding calculations. In particular, we
highlight the relation between the non-integer particle-number partition scheme
and the resulting embedding errors. Finally, we provide a discussion of the
implications of the present theory for the derivative discontinuity issue and
the calculation of chemical reactivity descriptors.

Chemical Physics;Other Condensed Matter