Shankar P. Das

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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(More)
Exact equations of motion for the microscopically defined collective density ρ(x,t) and the momentum density ĝ(x,t) of a fluid have been obtained in the past starting from the corresponding Langevin equations representing the dynamics of the fluid particles. In the present work we average these exact equations of microscopic dynamics over the local(More)
The importance of the presence of a small fraction of vacancies in a crystal structure is demonstrated from considerations of thermodynamic stability. We include in the density functional theory the effects due to the distortion of the lattice structure surrounding the vacancy and show that the free energy is less when vacancies are present. Near freezing(More)
The frequency dependent shear modulus G(omega) for a simple liquid shows strongly stretched behavior and the stretching exponent increases with decrease of temperature. This unconventional behavior was reported earlier in Phys. Rev. Lett. 73, 963 (1994) from experiments on simple liquids. We demonstrate here that this is a feature of the characteristic(More)
We have studied the relation between the structural relaxation and the frequency-dependent thermal response or the specific heat, c(p)(omega), in a supercooled liquid. The mode coupling theory (MCT) results are used to obtain c(p)(omega) corresponding to different wave vectors. Due to the two-step relaxation process present in the MCT, an extra peak, in(More)
In this paper, we address the question of whether aging in the nonequilibrium glassy state is controlled by the equilibrium alpha-relaxation process, which occurs at temperatures above T(g) . Recently, Lunkenheimer [Phys. Rev. Lett. 95, 055702 (2005)] proposed a model for the glassy aging data of dielectric relaxation using a modified(More)
The ergodicity-nonergodicity (ENE) transition of the self-consistent mode-coupling theory (MCT) is marked by the point at which the time correlation of collective density fluctuations is not zero in the long-time limit. The nonergodic state, reaching beyond the ENE transition of simple MCT, is characterized by a finite shear modulus. The MCT, formulated in(More)
The heterogeneous features of the supercooled state over different time regimes are explored in a self-consistent mode-coupling mode. The exponent a for the mean-square displacement <r(2)(t)> approximately t(a), of a tagged particle is computed. The non-Gaussian parameter alpha(2)(t) shows a peak in the short time regime in addition to a second peak over(More)
Despite its appeal, real and simulated glass forming systems do not undergo an ergodic-nonergodic (ENE) transition. We reconsider whether the fluctuating nonlinear hydrodynamics (FNH) model for this system, introduced by us in 1986, supports an ENE transition. Using nonperturbative arguments, with no reference to the hydrodynamic regime, we show that the(More)
We incorporate the role of free volume in the density function of the amorphous structure and study its effects on the stability of such structures. The Density Functional Theory is used to explore this “Free Volume Model” of the supercooled structures. The Free energy minimization is carried out using the void concentration as a variational parameter. A(More)