  The properties of molecules and materials containing light nuclei are
affected by their quantum mechanical nature. Modelling these quantum nuclear
effects accurately requires computationally demanding path integral techniques.
Considerable success has been achieved in reducing the cost of such simulations
by using generalized Langevin dynamics to induce frequency-dependent
fluctuations. Path integral generalized Langevin equation methods, however,
have this far been limited to the study of static, thermodynamic properties due
to the large perturbation to the system's dynamics induced by the aggressive
thermostatting. Here we introduce a post-processing scheme, based on analytical
estimates of the dynamical perturbation induced by the generalized Langevin
dynamics, that makes it possible to recover meaningful time correlation
properties from a thermostatted trajectory. We show that this approach yields
spectroscopic observables for model and realistic systems which have an
accuracy comparable to much more demanding approximate quantum dynamics
techniques based on full path integral simulations.
