{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"44066b468d0919a21e35be2cfc5cce07adb66d5ed59d734cb9818017668438b4","created":"2026-10-03T07:17:58Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"f1e313ee6bfc17a976e6fcac037a47f446052753cc8a9c4027a1413eaf1625db","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"chem.reaction-dynamics.water-isotope-effects","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"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.","posed_since":"","precise":"Using path-integral simulations on a potential of coupled-cluster quality not fitted to isotope data, compute the H2O to D2O 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":null,"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 H2O versus D2O differences from first-principles quantum 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