  By paying special attention to the fact that the doped holes induce
deformation of CuO6 octahedrons (or CuO5 pyramids) in cuprate superconductors,
we develop a non-rigid band theory treating doping-induced alterations of
energy-band structures in copper oxide superconductors. Thanks to this theory,
we obtain a complete picture of the doping-induced alteration in the electronic
structure of La2CuO4, from the spin-disordered insulating phase to the metallic
phase. We conclude that the Fermi surface structure of this cuprate in the
underdoped region consists of Fermi pockets in the antinodal region and Fermi
arcs in the nodal region, and thus that the origin of a so-called pseudogap is
closely related to the existence of Fermi pockets. Moreover, we show that the
carriers on the Fermi pockets contribute to the phonon mechanism in d-wave
superconductivity. Finally, we discuss how one will be able to find higher Tc
materials, based on the conclusions mentioned above.
