title: Two-dimensional percolation at the free water surface and its relation with the surface tension anomaly of water.
abstract: The percolation temperature of the lateral hydrogen bonding network of the molecules at the free water surface is determined by means of molecular dynamics computer simulation and identification of the truly interfacial molecules analysis for six different water models, including three, four, and five site ones. The results reveal that the lateral percolation temperature coincides with the point where the temperature derivative of the surface tension has a minimum. Hence, the anomalous temperature dependence of the water surface tension is explained by this percolation transition. It is also found that the hydrogen bonding structure of the water surface is largely model-independent at the percolation threshold; the molecules have, on average, 1.90 ± 0.07 hydrogen bonded surface neighbors. The distribution of the molecules according to the number of their hydrogen bonded neighbors at the percolation threshold also agrees very well for all the water models considered. Hydrogen bonding at the water surface can be well described in terms of the random bond percolation model, namely, by the assumptions that (i) every surface water molecule can form up to 3 hydrogen bonds with its lateral neighbors and (ii) the formation of these hydrogen bonds occurs independently from each other.
authors.affiliation: Department of Physics, University of Rome "Tor Vergata," via della Ricerca Scientifica 1, I-00133 Rome, Italy and Institut für Computergestützte Biologische Chemie, University of Vienna, Währinger Strasse 17, A-1090 Vienna, Austria.
authors.forename: Marcello
authors.initials: M
authors.lastname: Sega
authors.affiliation: MTA-BME Research Group of Technical Analytical Chemistry, Szt. Gellért tér 4, H‑1111 Budapest, Hungary.
authors.forename: George
authors.initials: G
authors.lastname: Horvai
authors.affiliation: Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szt. Gellért tér 4, H-1111 Budapest, Hungary.
authors.forename: Pál
authors.initials: P
authors.lastname: Jedlovszky
mesh_terms: D003198:Computer Simulation; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D013500:Surface Tension; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D006859:Hydrogen