Papers by sarika bhattacharyya
Orientational relaxation (OR) in a viscous, glassy liquid is investigated by carrying out extensi... more Orientational relaxation (OR) in a viscous, glassy liquid is investigated by carrying out extensive NPT molecular dynamics simulations of isolated ellipsoids in a glass forming binary mixture. Near the glass transition, the OR occurs mainly via correlated hopping, sometimes involving participation of several neighboring atoms, placed in a ring like tunnel. In the glassy state, hopping is found to be accompanied by larger fluctuations in the total energy and the volume of the system. Both orientational and translational hopping are found to be gated, restricted primarily by the entropic bottlenecks, with orientation becoming increasingly slower than translation as the pressure is increased. OR is heterogeneous, with a wide distribution of decay times. PACS numbers: 61.20.Lc, 64.70.Pf 1
The Journal of Chemical Physics, 1997
A theoretical study of vibrational dephasing of molecular vibrations in Liquids is presented with... more A theoretical study of vibrational dephasing of molecular vibrations in Liquids is presented with an aim to understand the experimentally observed sub-quadratic quantum number (n) dependence bf the vibrational dephasing rate, in systems like CH3I and CHCl3 and their deuterated ...
We carry out extensive molecular dynamics ͑MD͒ simulations of translation and rotation of spheroi... more We carry out extensive molecular dynamics ͑MD͒ simulations of translation and rotation of spheroids in the suspension of spheres, for a wide range of values of the aspect ratio, ranging from the extreme limits of long rodlike molecules to the disc-shaped ones. While diffusion is anisotropic in short times ͑compared to the orientational correlation time͒, it is isotropic in the very long time and the ratio of the two components of short time translational diffusion ͑D ʈ and D Ќ , where ʈ and Ќ refer to the motion parallel and perpendicular to the major axis͒ scales with the aspect ratio over a large range of . For thin discs, the preferred mode of motion is in the plane of the disc. The oblates show a very long-time orientational correlation which is reflected by the slow decay of its time correlation function. The correlation time becomes progressively longer and finally diverges as the spherical limit is approached. This is expected because the angular momentum is conserved in the ...
Journal of Physics: Condensed Matter
Journal of Chemical Sciences
In this paper we explore the validity of the Rosenfeld and the Dzugutov relation for the Lennard-... more In this paper we explore the validity of the Rosenfeld and the Dzugutov relation for the Lennard-Jones (LJ) system, its repulsive counterpart, the WCA system and a network forming liquid, the NTW model. We find that for all the systems both the relations are valid at high temperature regime with an universal exponent close to 0.8. Similar to that observed for the simple liquids, the LJ and the WCA systems show a breakdown of the scaling laws at the low temperature regime. However for the NTW model, which is a simple liquid, these scaling laws are valid even at lower temperature regime similar to that found for ionic melts. Thus we find that the NTW model has mixed characteristics of simple liquids and ionic melts. Our study further reveals a quantitative relationship between the Rosenfeld and the Arrhenius relations. For strong liquids, the validity of the Rosenfeld relation in the low temperature regime is connected to it following the Arrhenius behaviour in that regime. Finally we explore the role of pair entropy and residual multiparticle entropy in the dynamics as a function of fragility of the systems.
The Journal of Chemical Physics, 2016
In this paper, we present a study of supercooled liquids interacting with the Lennard Jones poten... more In this paper, we present a study of supercooled liquids interacting with the Lennard Jones potential and the corresponding purely repulsive (Weeks-Chandler-Andersen) potential, over a range of densities and temperatures, in order to understand the origin of their different dynamics in spite of their structures being similar. Using the configurational entropy as the thermodynamic marker via the Adam Gibbs relation, we show that the difference in the dynamics of these two systems at low temperatures can be explained from thermodynamics. At higher densities both the thermodynamical and dynamical difference between these model systems decrease, which is quantitatively demonstrated in this paper by calculating different parameters. The study also reveals the origin of the difference in pair entropy despite the similarity in the structure. Although the maximum difference in structure is obtained in the partial radial distribution function of the B type of particles, the rdf of AA pairs and AB pairs gives rise to the differences in the entropy and dynamics. This work supports the observation made in an earlier study [A. Banerjee et al., Phys. Rev. Lett. 113, 225701 (2014)] and shows that they are generic in nature, independent of density.
The Journal of Chemical Physics, 2016
We present a comparative study of the glass forming ability of binary systems with varying compos... more We present a comparative study of the glass forming ability of binary systems with varying composition, where the systems have similar global crystalline structure (CsCl+fcc). Biased Monte Carlo simulations using umbrella sampling technique shows that the free energy cost to create a CsCl nucleus increases as the composition of the smaller particles are decreased. We find that the systems with comparatively lower free energy cost to form CsCl nucleus exhibit more pronounced pre-crystalline demixing near the liquid/crystal interface. The structural frustration between the CsCl and fcc crystal demands this demixing. We show that closer to the equimolar mixture the entropic penalty for demixing is lower and a glass forming system may crystallize spontaneously when seeded with a nucleus. This entropic penalty as a function of composition shows a non-monotonic behavior with a maximum at a composition similar to the well known Kob-Anderson (KA) model. Although the KA model shows the maximum entropic penalty and thus maximum frustration against CsCl formation, it also shows a strong tendency towards crystallization into fcc lattice of the larger "A" particles which can be explained from the study of the energetics. Thus for systems closer to the equimolar mixture although it is the requirement of demixing which provides their stability against crystallization, for KA model it is not demixing but slow dynamics and structural frustration caused by the locally favored structure around the smaller "B" particles which make it a good glass former. Although the glass forming binary systems studied here are quite similar, differing only in composition, we find that their glass forming ability cannot be attributed to a single phenomena.
The Journal of Chemical Physics, 2015
We analyze the dynamics of model supercooled liquids in a temperature regime where predictions of... more We analyze the dynamics of model supercooled liquids in a temperature regime where predictions of mode coupling theory (MCT) are known to be valid qualitatively. In this regime, the Adam-Gibbs (AG) relation, based on an activation picture of dynamics also describes the dynamics satisfactorily, and we explore the mutual consistency and interrelation of these descriptions. Although entropy and dynamics are related via phenomenological theories, the connection between MCT and entropy has not been argued for. In this work we explore this connection and provide a microscopic derivation of the phenomenological Rosenfeld theory. At low temperatures the overlap between MCT power law regime and AG relation implies that the AG relation predicts an avoided divergence at T c , the origin of which is traced back to the vanishing of pair configurational entropy, which we find occurs at the same temperature. We also show that the residual multiparticle entropy plays an important role in describing the relaxation time.
Orientational relaxation (OR) in a viscous, glassy liquid is investigated by carrying out extensi... more Orientational relaxation (OR) in a viscous, glassy liquid is investigated by carrying out extensive NPT molecular dynamics simulations of isolated ellipsoids in a glass forming binary mixture. Near the glass transition, the OR occurs mainly via correlated hopping, sometimes involving participation of several neighboring atoms, placed in a ring like tunnel. In the glassy state, hopping is found to be accompanied by larger fluctuations in the total energy and the volume of the system. Both orientational and translational hopping are found to be gated, restricted primarily by the entropic bottlenecks, with orientation becoming increasingly slower than translation as the pressure is increased. OR is heterogeneous, with a wide distribution of decay times.
The Journal of Physical Chemistry B, 2015
We study the diffusion of small solute particles through solvent by keeping the solute-solvent in... more We study the diffusion of small solute particles through solvent by keeping the solute-solvent interaction repulsive and varying the solvent properties. The study involves computer simulations, development of a new model to describe diffusion of small solutes in a solvent, and also mode coupling theory (MCT) calculations. In a viscous solvent, a small solute diffuses via coupling to the solvent hydrodynamic modes and also through the transient cages formed by the solvent. The model developed can estimate the independent contributions from these two different channels of diffusion. Although the solute diffusion in all the systems shows an amplification, the degree of it increases with solvent viscosity. The model correctly predicts that when the solvent viscosity is high, the solute primarily diffuses by exploiting the solvent cages. In such a scenario the MCT diffusion performed for a static solvent provides a correct estimation of the cage diffusion.
Advances in Chemical Physics, 2001
... For Authors. Mode Coupling Theory Approach to the Liquid-State Dynamics. I. Prigogine 2,3 ,; ... more ... For Authors. Mode Coupling Theory Approach to the Liquid-State Dynamics. I. Prigogine 2,3 ,; Stuart A. Rice 4. Biman Bagchi,; Sarika Bhattacharyya. Published Online: 14 MAR 2007. DOI: 10.1002/9780470141762.ch2. Copyright © 2001 by John Wiley & Sons, Inc. Book Title. ...
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 2000
The self-diffusion coefficient of a tagged molecule is known to exhibit a weak mass dependence, e... more The self-diffusion coefficient of a tagged molecule is known to exhibit a weak mass dependence, especially for solutes with size comparable to or larger than the size of the solvent molecules. Sometimes this mass dependence can be fitted to a power law, with a small exponent, less than 0.1. This weak mass dependence has often been considered as supportive of the hydrodynamic picture (that is, the Stokes-Einstein relation) of diffusion rather than the kinetic theory approach, which predicts a stronger mass dependence, for example, via the Enskog theory. Neither can explain the weak power-law mass dependence. In order to understand this, we have carried out a mode coupling theory (MCT) analysis of diffusion. It is found that a straightforward application of the existing mode coupling theory expressions lead to an inaccurate mass dependence-it predicts an increase of diffusion coefficient with an increase of the mass. We find that this is because of the inadequate description of the in...
Physical Review Letters, 2014
We present a study of two model liquids with different interaction potentials, exhibiting similar... more We present a study of two model liquids with different interaction potentials, exhibiting similar structure but significantly different dynamics at low temperatures. By evaluating the configurational entropy, we show that the differences in the dynamics of these systems can be understood in terms of their thermodynamic differences. Analyzing their structure, we demonstrate that differences in pair correlation functions between the two systems, through their contribution to the entropy, dominate the differences in their dynamics, and indeed overestimate the differences. Including the contribution of higher order structural correlations to the entropy leads to smaller estimates for the relaxation times, as well as smaller differences between the two studied systems.
In low temperature supercooled liquid, below the ideal mode coupling theory transition temperatur... more In low temperature supercooled liquid, below the ideal mode coupling theory transition temperature, hopping and continuous diffusion are seen to coexist. We present a theory which incorporates interaction between the two processes and shows that hopping can induce continuous diffusion in the otherwise frozen liquid. Several universal features arise from nonlinear interactions between the continuous diffusive dynamics (described here by the mode coupling theory (MCT)) and the activated hopping (described here by the random first order transition theory). We apply the theory to real systems (Salol) to show that the theory correctly predicts the temperature dependence of the nonexponential stretching parameter, β, and the primary α relaxation timescale, τ. The study explains why, even below the ergodic to non-ergodic transition, the dynamics is well described by MCT. The non-linear coupling between the two dynamical processes modifies the relaxation behavior of the structural relaxation from what would be predicted by a theory with a complete static Gaussian barrier distribution in a manner that may be described as a facilitation effect. Furthermore, the theory explains the observed variation of the stretching exponent β with the fragility parameter, D. c −γ , (γ > 0). T f it c is referred to as the MCT transition temperature. Above T f it c , MCT is found to explain many experimental results [6, 7, 8, 9, 10], and below T f it c , the MCT description of continuous diffusion breaks down. It is conjectured that this breakdown is due to the ergodic to non-ergodic transition in the dynamics and below T f it c activated dynamics becomes a dominant mode of transport. However in an elegant work, Burmer and Reichman [11] (BR) have recently shown that the idealized MCT breaks down at a
As a liquid is progressively supercooled an intriguing weakening of the wavenumber (q) dependence... more As a liquid is progressively supercooled an intriguing weakening of the wavenumber (q) dependence of the structural relaxation time τ (q) in the large q limit is observed both in experiments and simulation studies. Neither the continuous Brownian diffusive dynamics nor the discontinuous activated events can alone explain the anomalous wavenumber dependence. Here we use our recently developed theory that unifies the mode coupling theory (MCT) for continuous dynamics and the random first order transition theory (RFOT) treatment of activated discontinuous motion as a nucleation (instanton) process, to understand the wavenumber dependence of density relaxation. The predicted smooth change in mechanism of relaxation from diffusive to activated, in the crossover regime, is wavevector dependent and is eventually responsible for sub-quadratic, almost linear, q dependence of the relaxation time.
We present a theoretical analysis of the dynamic structure factor (DSF) of a liquid at and below ... more We present a theoretical analysis of the dynamic structure factor (DSF) of a liquid at and below the mode coupling critical temperature Tc, by developing a self-consistent theoretical treatment which includes the contributions both from continuous diffusion, described using general two coupling parameter (F12) mode coupling theory (MCT), and from the activated hopping, described using the random first order transition (RFOT) theory, incorporating the effect of dynamical heterogeneity. The theory is valid over the whole temperature plane and shows correct limiting MCT like behavior above Tc and goes over to the RFOT theory near the glass transition temperature, Tg. Between Tc and Tg, the theory predicts that neither the continuous diffusion, described by pure mode coupling theory, nor the hopping motion alone suffices but both contribute to the dynamics while interacting with each other. We show that the interplay between the two contributions conspires to modify the relaxation behavior of the DSF from what would be predicted by a theory with a complete static Gaussian barrier distribution in a manner that may be described as a facilitation effect. Close to Tc, coupling between the short time part of MCT dynamics and hopping reduces the stretching given by the F12-MCT theory significantly and accelerates structural relaxation. As the temperature is progressively lowered below Tc, the equations yield a crossover from MCT dominated regime to the hopping dominated regime. In the combined theory the dynamical heterogeneity is modified because the low barrier components interact with the MCT dynamics to enhance the relaxation rate below Tc and reduces the stretching that would otherwise arise from an input static barrier height distribution. Many of these results can be explained from an analytical treatment of the combined equation of motion.
The Journal of Physical Chemistry B, 2003
... Sarika M. Bhattacharyya, Zhen-Gang Wang,* and Ahmed H. Zewail*. Laboratory for Molecular Scie... more ... Sarika M. Bhattacharyya, Zhen-Gang Wang,* and Ahmed H. Zewail*. Laboratory for Molecular Sciences and Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125. J. Phys. Chem. ...
The Journal of Physical Chemistry B, 1998
An understanding of the effect of specific solute-solvent interactions on the diffusion of a solu... more An understanding of the effect of specific solute-solvent interactions on the diffusion of a solute probe is a long standing problem of physical chemistry. In this paper a microscopic treatment of this effect is presented. The theory takes into account the modification of the ...
Proceedings of the National Academy of Sciences, 2008
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Papers by sarika bhattacharyya