  We consider a pentagon chain described by a Hubbard type of model considered
under periodic boundary conditions. The system i) is placed in an external
magnetic field perpendicular to the plane of the cells, and ii) is in a site
selective manner under the action of an external electric potential. In these
conditions we show in a non-approximated manner that the physical properties of
the system can be qualitatively changed. The changes cause first strong
modifications of the band structure of the system created by the one-particle
part of the Hamiltonian, and second, considerably redraw the emergence domains
of ordered phases. We exemplify this by deducing ferromagnetic ground states in
the presence of external fields in two different domains of the parameter
space.
