  We demonstrate the accuracy and efficiency of a recently introduced approach
to account for nuclear quantum effects (NQE) in molecular simulations: the
adaptive Quantum Thermal Bath (adQTB). In this method, zero point energy is
introduced through a generalized Langevin thermostat designed to precisely
enforce the quantum fluctuation-dissipation theorem. We propose a refined adQTB
algorithm with improved accuracy and we report adQTB simulations of liquid
water. Through extensive comparison with reference path integral calculations,
we demonstrate that it provides excellent accuracy for a broad range of
structural and thermodynamic observables as well as infrared vibrational
spectra. The adQTB has a computational cost comparable to classical molecular
dynamics, enabling simulations of up to millions of degrees of freedom.
