  Thermodynamics of dissipative quantum systems with double-well potentials is
studied by the path-integral Monte Carlo (PIMC) method without truncation to
the two-state model. For efficient simulation at low temperatures, we develop a
new scheme of local update based on approximate decomposition of the Boltzmann
weight to the Gaussian distributions. Localization transition induced by ohmic
dissipation is clarified numerically for arbitrary potential barriers.

Statistical Mechanics