AbstractThe interplay of the electron–phonon interaction and of the double and super‐exchange magnetic effects in the La1–xCaxMnO3 perovskites with 0 < x < 0.5 is studied. It is shown that treating the electron–phonon interaction in a fully quantum manner in the intermediate electron–phonon coupling regime a charge density instability occurs near the metal–insulator transition, induced by either temperature or hole doping. Also the effects of the magnetic field and the oxygen isotope substitution on the phase diagram, the electron–phonon correlation function and the infrared absorption at x = 0.3 is studied. The lattice displacements show a strong correlation with the conductivity and the magnetic properties of the system. Finally the conductivity spectra are characterized by a marked sensitivity to the external parameters near the phase boundary.