Structure and dynamics of high and low density water molecules in the liquid and supercooled regimes

S.R. ACCORDINO; J.A. RODRIGUEZ FRIS; G.A. APPIGNANESI; J.M. MONTES DE OCA; D.C. MALASPINA

The European Physical Journal E

EDP Sciences, Springer Science+Business Media, Società Italiana di Fisica

Lugar: Berlin; Año: 2016 vol. 39

1292-8941

By combining the local structure index with potential energy minimisations we study the localenvironment of the water molecules for a couple of water models, TIP5P-EW and SPC/E, in order tocharacterise low and high density ?species?. Both models show a similar behaviour within the supercooledregime, with two clearly distinguishable populations of unstructured and structured molecules, the fractionof the latter increasing with supercooling. However, for TIP5P-EW, we find that the structured componentvanishes quickly at the normal liquid regime (above the melting temperature) probably due to the domi-nance of the entropic weight of the unstructured state, since its melting temperature is higher and muchcloser to the experimental one. For both models we also show that, while the structured state is ratherunique (or a set of closely related structures), the representative arrangements of the unstructured statedepend notably on temperature, thus pointing to the fact that this state is in fact of a plethora of differentdistorted structures (a high entropy state) as suggested by the two-order parameter model. Finally, we linkstructure to dynamics by showing that there exists a strong correlation between structural fluctuationsand dynamics in the supercooled state with spatial correlations in both static and dynamic quantities.