Polarons in one‐dimensional molecular chains with intermolecular and intramolecular vibrations

Polarons are investigated in a model for one‐dimensional molecular chains involving both acoustical and optical lattice vibrations, as found in diatomic chains. With the help of a specific ansatz for low‐lying quasiparticles, a continuum limit approximation sustains the existence of analytical solutions to the model. The dispersion energy as well as the effective mass of low‐lying electronic states in the presence of the two lattice mode‐induced polaronic quasiparticle, are derived analytically. It is found that the band effective mass is strongly enhanced by a factor depending on the two electron–lattice coupling constants. A test of stability of the analytical shapes of the three long‐wavelength excitations is carried out numerically by following their simultaneous propagation throughout the molecular lattice. The long‐wavelength polaron appears to be very stable within an acceptable range of values of the electron wave vector and propagates faster and faster as one moves from the groundstate toward mid‐band states. However, the accompanying kink and pulse soliton deformations are always slower consistently with the adiabatic considerations underlying the quasi‐classical treatment followed in this work. In addition, the kink component of the lattice deformation tends to become unstable at relatively large electronic wave vectors, while the polaron and in turn the optical lattice deformation are more and more stable, traducing dominant optical modes of the lattice in the process of formation of polaron. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008