  We study the electronic structure of the SmFeAsO(1-x)F(x) alloy by means of
first-principle calculations. We find that, contrary to common believe,
F-doping does not change the charge balance between electrons and holes
free-carriers in SmFeAsO(1-x)F(x). For energies within a narrow energy range
across E_F, the effect of F-doping on the band structure dispersion is tiny in
both the paramagnetic and stripe antiferromagnetic phase. The charge balance
between the conducting FeAs-layer and the SmO(1-x)F(x) charge reservoir layer
is not influenced by the compositional change. The additional charge carried by
fluorine, with respect to the oxygen, is compensated by a change in the
oxidation state of the Sm ion from 3+ to 2+. A comparison with the
SmFe(1-x)Co(x)AsO system shows that such charge compensation by the Sm ion is
not shared by donors substituting at the Fe site.
