We use a simple mean field scheme to compute the polarization energy of an excess electron in amorphous polyethylene that allows us to study dynamical properties. Nonadiabatic simulations of an excess electron in amorphous polyethylene at room temperature show the spontaneous formation of localized small polaron states in which the electron is confined in a spherically shaped region with a typical dimension of 5 A. We compute the self-trapping energy to be -0.06+/-0.03 eV, with a lifetime on the time scale of a few tens of picoseconds. (C) 2004 American Institute of Physics.