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These differences come only from the quantum motion of nuclei, so they test whether simulations treat that motion correctly.","posed_since":"","precise":"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.","problem_ref":"ea150b8f16f7eadb14fbfa2c8c9daa6bf94923174d4a61727893c235ca78829b","references":"","settled_by":"Converged path-integral free-energy and dynamics calculations on an ab initio-quality many-body potential compared with measured isotope shifts.","status_note":"","title":"Quantitative $\\mathrm{H_2O}$ versus $\\mathrm{D_2O}$ differences from first-principles quantum 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