Nuclear quantum effects
have significant contributions to thermodynamic
quantities and structural properties; furthermore, very expensive
methods are necessary for their accurate computation. In most calculations,
these effects, for instance, zero-point energies, are simply neglected
or only taken into account within the quantum harmonic oscillator
approximation. Herein, we present a new method, Generalized Smoothed
Trajectory Analysis, to determine nuclear quantum effects from molecular
dynamics simulations. The broad applicability is demonstrated with
the examples of a harmonic oscillator and different states of water.
Ab initio molecular dynamics simulations have been performed for ideal
gas up to the temperature of 5000 K. Classical molecular dynamics
have been carried out for hexagonal ice, liquid water, and vapor at
atmospheric pressure. With respect to the experimental heat capacity,
our method outperforms previous calculations in the literature in
a wide temperature range at lower computational cost than other alternatives.
Dynamic and structural nuclear quantum effects of water are also discussed.