Quantitative $\mathrm{H_2O}$ versus $\mathrm{D_2O}$ differences from first-principles quantum simulation
In plain words
Heavy water, in which hydrogen is replaced by deuterium, has its density maximum near 11 C instead of 4 C and is about 23 percent more viscous. These differences come only from the quantum motion of nuclei, so they test whether simulations treat that motion correctly.
Precise statement
Using path-integral simulations on a potential of coupled-cluster quality not fitted to isotope data, compute the $\mathrm{H_2O}$ to $\mathrm{D_2O}$ shifts of the temperature of maximum density (277.13 K versus about 284.3 K), the melting temperature (273.15 K versus about 276.97 K) and the viscosity ratio at 298 K (about 1.23), and decompose each into the competing quantum effects (hydrogen-bond weakening by intermolecular zero-point motion versus strengthening by O-H stretch delocalization). An answer is computed shifts within 1 K and 5 percent of experiment with the decomposition.
What would settle it
Converged path-integral free-energy and dynamics calculations on an ab initio-quality many-body potential compared with measured isotope shifts.
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See also
- Related Location of water's liquid-liquid critical point
- Related Origin of the thermodynamic anomalies of supercooled water
- Related Solvation structure and infrared signature of the excess proton
- Related Rate-limiting step of proton transport in liquid water
- Related Accurate quantum time-correlation functions for anharmonic liquids
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