Nuclear Quantum Effects in Water

A path-integral Car-Parrinello molecular dynamics simulation of liquid water and ice is performed. It is found that the inclusion of nuclear quantum effects systematically improves the agreement of first-principles simulations of liquid water with experiment. In addition, the proton momentum distribution is computed utilizing a recently developed open path-integral molecular dynamics methodology. It is shown that these results are in good agreement with experimental data.

Figure 1

The OO (top) and OH (bottom) RDFs in liquid water from an open PI CPMD simulation at 300 K (solid line) and standard CPMD simulations at 300 K (dashed line) and 330 K (dotted line) are reported with neutron [4] (circles) and recent joint neutron/x-ray data [5] (triangles) that utilize different x-ray input for $A$ [6] and $B$ [7].

Figure 2

The dipole moment distribution of the full PI simulation (solid line), corrected PI simulation (dotted line), and standard (dashed line) simulation of water at 300 K.

Figure 3

The radial proton momentum distribution is reported in the liquid (solid line) and solid (dashed line) phases and plotted against the experimental liquid (circles) and solid (triangles) curves [2], as well as the Boltzmann distribution (dashed line) at 300 K. The insets (a) and (b) depict the tail of the liquid (solid line) and solid (dashed line) distributions, in the simulation and experiment, respectively.