  The chemical influence in the phase separation phenomenon that occurs in
perovskite manganites is discussed by means of ab initio calculations.
Supercells have been used to simulate a phase separated state, that occurs at
Ca concentrations close to the localized to itinerant crossover. We have first
considered a model with two types of magnetic ordering coexisting within the
same compound. This is not stable. However, a non-isotropic distribution of
chemical dopants is found to be the ground state. This leads to regions in the
system with different effective concentrations, that would always accompany the
magnetic phase separation at the same nanometric scale, with hole-rich regions
being more ferromagnetic in character and hole-poor regions being in the
antiferromagnetic region of the phase diagram, as long as the system is close
to a phase crossover.
