  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.
