Convergence with respect to imaginary-time discretization (ie, the number of ring-polymer
beads) is an essential part of any path-integral-based molecular dynamics (MD) calculation.
However, an unfortunate property of existing non-preconditioned numerical integration
schemes for path-integral molecular dynamics—including essentially all existing ring-
polymer molecular dynamics (RPMD) and thermostatted RPMD (T-RPMD) methods—is that
for a given MD time step, the overlap between the exact ring-polymer Boltzmann–Gibbs …