Localization of quasiparticles in extended atomic systems is known to be driven by disorder, point defects or distortions of the ionic lattice. Herein we give first-principles theoretical computational evidence that localization can also appear as a purely electronic effect in otherwise perfectly ordered periodic structures. In a brand of density functional theory, devoid of localization/delocalization errors, excitations localize in long finite strands of perfectly ordered transpolyacetyline and polythiophene polymers. This is caused by exchange induced spontaneous continuous symmetry breaking of the ionic lattice's translational invariance. Ionization potentials, optical absorption peaks, excitonic binding energies and the optimally-tuned range parameter itself all become independent of polymer length once it exceeds a system-dependent critical localization length scale. The energy associated with this type of localization is estimated to be on the order of 0.5eV. This first-principles finding shows, for the first time, that charge localization is not caused by lattice distortion but rather, causes it. These results help explaining experimental findings that polarons form instantaneously after exposure to ultrafast light pulses.