8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P2.50Tue 611:23-14:00Correlations in diffusional motion of water molecules:computer simulationGeorge Malenkov, 1 Yu. I. Naberukhin, 2 and V. P. Voloshin 21 A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Leninsky Prospect,31, 119991, Moscow, Russian Federation2 Russian Academy of Sciences (Siberian division), Novosibirsk, Russian FederationIn order to reveal correlations in diffusional motion of water molecules molecular dynamics ofwater (several thousands of molecules, up to 10000 in periodic cubic cell) at various temperatureswas performed. Correlation of displacement vectors for the pairs of water molecules whoseoxygen-oxygen distance r i OO in the initial configurations lay within certain limits was studied.Several functions describing these correlations were proposed and calculated. Behaviour of correlatorDP =< [r i (t) −r i (0)][r k (t) −r k (0)] > (scalar product of displacement vectors of two watermolecules) is rather unusual. The curves DP(t) increase with time and flatten at several hundredsof pc. Corresponding correlation coefficients CC (cosines of the angles between the vectors) decreasewith time but do not reach zero even several ns after the start of simulation. The flatteningof the curves DP(t) is the results of the subtle compensation of the decrease of mean cosine valuesby the increase of the length of the vectors. The height of the flat portions of the DP(t) curvesdecreases with the increase of riOO values, but such behaviour of this function is still observedwhen r i OO is larger than 10 å. When we calculated DP and CC for randomly moving particlesboth functions were close to zero all the time. It means that long-lived correlations in displacementsof molecules separated by large distances do exist in water and is not artifact of simulation.Behaviour of other functions depending on the displacements of two molecules for various r i OOvalues was also studied. All of them count in favour of long-range correlations. Moreover, suchfunction as < |r ik (t) − r ik (0)| > (change of the modulus of the distance between oxygen atoms)exhibits non trivial dependence on r i OO. This fact also needs study and explanation. The workwas supported by Russian Foundation for basic research (project No 09-03-00419)50