  We apply the displaced-oscillator variational ansatz to the Caldeira-Leggett
model for a quantum particle in a one-dimensional box described by a
tight-binding chain. We focus on the case of an Ohmic environment and study the
phase diagram for different chain lengths. At zero temperature there is a phase
transition to a localized phase when the number of sites is even. At finite
temperature, a transition from a coherent to an incoherent regime is predicted
for all the chain lengths considered. Finally, the results are compared to
those obtained with numerical techniques.
