Charanbir Kaur

Heterogeneities in supercooled liquids: a density-functional study.

A metastable state, characterized by a low degree of mass localization, is identified using density-functional theory (DFT). This free energy minimum, located through the proper evaluation of competing terms in the free energy functional, is independent of the specific form of the DFT used. Computer simulation results on particle motion indicate that this heterogeneous state corresponds to the deeply supercooled state.

Nature of the entropy versus self-diffusivity plot for simple liquids

The empirical relation (D(*))(alpha) = a exp[S] between the self-diffusion coefficient D(*) and the excess entropy S of a liquid is studied here in the context of theoretical model calculation. The coefficient alpha is dependent on the interaction potential and shows a crossover at an intermediate density, where cooperative dynamics become more important. Around this density a departure from the Stokes-Einstein relation is also observed. The above relation between entropy and diffusion is also tested for the scaled total diffusion coefficient in a binary mixture.

Effect of attractive interactions on tagged particle dynamics

We study tagged particle dynamics in a one-component simple liquid characterized by the Lennard-Jones (LJ) interaction potential. Extended mode coupling theory is used to obtain the correlation function which feeds back on the dynamics of the self-correlations. The cooperative dynamical effects are studied by evaluating various properties of tagged particle motion as influenced by the collective dynamics. Comparison between the results obtained for particles with purely repulsive interactions like the truncated LJ potential (or the hard-sphere interaction) and that of the full LJ potential are shown. The nature of the velocity autocorrelation function and the non-Gaussian variation of the van Hove self-correlation function is specifically highlighted here. The role of static structural input in the theory is considered especially in this regard.

Static and dynamical heterogeneities in supercooled liquids

We present here some features of supercooled liquids from both the structural and dynamical consideration. We discuss the existence of heterogenous structures characterized by weak mass localization. The analysis is done using the standard methods of density functional theory. The dynamics governing the supercooled states that lead to non-exponential relaxation of the time–correlation functions, are also studied. The dynamical heterogeneities are studied in terms of departure of the single particle dynamics from simple Gaussian behavior over intermediate timescales. Other relevant properties like the velocity auto-correlation function and the mean square displacement associated with the tagged particle dynamics are also computed.

Dynamics of a metastable liquid: comparison of results from two different approaches

One component Lennard-Jones fluid in the supercooled state has been recently studied by Angelani et al. [1] using the master equation approach to model the dynamics in the configuration space. Here we consider these results in the context of the extended mode coupling model (MCT). The crucial parameter related to the ergodicity restoring processes in the theoretical model is chosen such that transport coefficients calculated from the two approaches match. This parameter follows an activated behavior in order to produce the Arrhenius-type temperature dependence for the viscosity, as found in the master equation approach. Using the corresponding parameter values, we compute other dynamical properties of the supercooled LJ system.