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

Thu 811:10-14:00P8.47Reorientational dynamics in a supercooled molecularliquidGemma Sesé, 1 Jordi Ortiz de Urbina, 1 and Ricardo Palomar 11 Technical university of Catalonia-BarcelonaTech, Campus Nord UPC - Mòdul B4,c/ Jordi Girona 1-3 08034, Barcelona, SpainThe dynamics of a supercooled molecular liquid has been studied by means of molecular dynamicssimulations. The molecular model has been built from the one of methanol molecules, but lackingsites for hydrogen bonding. Then, rigid diatomic molecules with an associated dipole momenthave been considered. Time correlation functions that characterize translational dynamics ofthe system reveal the existence of three dynamic regimes at low temperatures [1]. Dynamicheterogeneities have been detected in this system [2]. The distribution of the dipole momentorientation has been evaluated at low temperatures. It has been found that the results can beextrapolated smoothly from the data obtained at higher temperatures. As for the dynamics,molecular reorientation can be described as a sequence of small amplitude angular steps. Ourresults are consistent with a picture where rotational motion is less dramatically hindered thantranslational diffusion. Angular velocity autocorrelation functions display a ”backscattering” area,which becomes more important upon cooling. Angular velocities have been used to compute theangular displacement vector [3]. Molecules that perform large displacements tend to perform largeangular displacements at low temperatures, when large time intervals are considered. Diffusioncoefficients have been evaluated from the slope of the mean square displacements at very longtimes. The Stokes-Einstein relation breaks for temperatures at which the spatial correlationsbetween molecules having similar mobilities become important [2]. The Stokes-Einstein-Debyerelation has also been checked by considering the rotational self-diffusion coefficients which havebeen obtained from the long-time slope of the rotational mean square displacement.[1] R. Palomar and G. Sesé, Phys. Rev. E 75, 011505 (2007).[2] R. Palomar and G. Sesé, J. Chem. Phys. 129, 064505 (2008).[3] S. Chong and W. Kob, Phys. Rev. Lett. 102, 025702 (2009).47