Electronic Kinetic Energy in the Polaron Ground State and the Location   of the Self-Trapping Transition
  In this paper we discuss the electronic kinetic energy in the ground state of the Holstein Hamiltonian in one space dimension using the Global-Local variational method together with perturbation theory at weak and strong coupling. The electronic kinetic energy is detailed over a broad region of the polaron parameter space, and is analyzed to accurately determine the location of the self-trapping transition. The self-trapping line so determined separates the small polaron regime from the large polaron regime, constituting a polaron phase diagram. 
A. H. Romero, David W. Brown, and Katja Lindenberg