Self-trapping on a dimer: Time-dependent solutions of a discrete nonlinear Schrödinger equation.

From the discrete nonlinear Schroedinger equation describing transport on a dimer we derive and solve a closed nonlinear equation for the site-occupation probability difference. Our results, which are directly relevant to specific experiments such as neutron scattering in physically realizable dimers, exhibit a transition from ''free'' to ''self-trapped'' behavior and illustrate features expected in extended systems, including soliton/polaron bandwidth reduction and the dependence of energy-transfer efficiency on initial conditions.