We performed both classical and path integral simulations of liquid water under ambient conditions for its thermodynamic properties. The simulations were carried out in constant temperature-constant pressure (NPT) ensembles. The calculated liquid water density, tetrahedral order parameter, and self-diffusion coefficient are given in Table . At 298 K and 1 atm, the calculated water density from classical MD is 1.002 g/cm 3 which is slightly higher than the experimental data. After nuclear quantum effects are considered in PIMD simulations, the density decreases to 0.997 g/cm -1 which reaches excellent agreement with experiment. This indicates the importance of zero-point energy and quantum delocalization in affecting the water structures and dimensions. Figure shows the OO, OH, and HH radial distribution functions (RDF) from both classical MD and PIMD NPT simulations. As seen, the RDFs from q-AQUA-pol are in good agreement with experimental measurement. For the OO RDF from classical MD simulation, the first and second peak appear at 2.80 and 4.47 Å, respectively, while the experimental peaks are at around 2.81 and 4.50 Å. The classical MD simulations with q-AQUA-pol potential correctly describe both H-bonded neighbors and non-H-bonded water molecules that occupy the interstitial space between H-bonded neighbors. Such agreement is further improved by the PIMD simulations, where the first and second peaks locate at 2.82 and 4.50