Structures of liquid and aqueous water isotopologues at ambient temperature from path integral simulations

Thomsen, B.  ; Shiga, Motoyuki   

The heavy hydrogen isotopes D and T are found in trace amounts in water, and they can when their concentration rises play an intricate role in modulating the physical properties of the liquid. We present an analysis of the microscopic structures of ambient light water (HO(l)), heavy water(DO(l)), TO(l), HDO(aq) and HTO(aq) studied by path integral molecular dynamics (PIMD). Unlike previous PIMD investigations of HO(l) and DO(l) [Chen et al., Phys. Rev. Lett., 2003, 91, 215503] [Machida et al., J. Chem. Phys., 2017, 148, 102324] we do find that DO(l) is more structured than HO(l), as is predicted by experiment. The agreement between experiment and our simulation for HO(l) and DO(l) allows us to accurately predict intra- and intermolecular structures of TO(l) HDO(aq) and HTO(aq). TO(l) is found to have a similar intermolecular structure to that of DO(l), while the intramolecular structure is more compact, giving rise to a smaller dipole moment that that if HO(l) and DO(l). For the mixed isotope species, HDO(aq) and HTO(aq), we find smaller dipole moments and less hydrogen bonds when compared with the pure species HO and DO. We can attribute this effect to the relative compactness of the mixed isotope species, which results in a lower dipole moment when compared to that of the pure species.