Nuclear quantum effects in molecular dynamics simulations of water

Thomsen, B.  ; Shiga, Motoyuki   

We report the results of our recent studies of ambient water and its isotopologues using ab initio path integral molecular dynamics simulations. These types of simulations allow us to describe the nuclear quantum effects (NQEs) with high accuracy which naturally manifests as the differences in properties and structure of HO, DO and other isotopologues of water. Here the inclusion of NQEs causes the liquid to be less structured that results from classical molecular dynamics simulations. With increasing isotope mass, going from HO to DO, we find in agreement with experimental observation that the liquid becomes more structured. For water molecules with mixed isotopologue composition, HDO and HTO, in HO we however find that the molecules and their surroundings are less structured. As water is heated up and reaches sub- and supercritical conditions the long-range modulation of the structure due to NQEs disappears. The short-range effects on especially the hydrogen bounded structures remain even at high temperatures. We will also briefly discuss our ongoing efforts to describe the dynamics of the ambient liquid, where both an explicit dependence of the mass of the particles and NQEs are important.