  The vibronic mixing by an odd-parity vibrational mode of two opposite-parity
nearly-degenerate electronic states at a molecular site may drive the small
polaron off-center. An associated electric dipole may occur due to broken
inversion symmetry which will exert an effect on the electric, optical and
transport properties of the host crystal. We first investigate the polaron
field in the non-interacting limit and then include Coulomb and dispersive
interactions leading to the formation of polaron pairs.
