02651nas a2200181 4500008004100000022001400041245010500055210006900160260008700229300002700316490000800343520189300351100002502244700002202269700002302291700003402314856012102348 2016 eng d a0021-960600aComposition dependence of the glass forming ability in binary mixtures: the role of demixing entropy0 aComposition dependence of the glass forming ability in binary mi a1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScJUL aArticle Number: 0345030 v1453 a

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 show that the free energy cost to create a CsCl nucleus increases as the composition of the smaller particles is decreased. We find that 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 when seeded with a nucleus. This entropic penalty as a function of composition shows a non-monotonic behaviour 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 the presence of the ``B'' particles make it a good glass former. The locally favoured structure around ``B'' particles is quite similar to the CsCl structure and the incompatibility of CsCl and fcc hinders the fcc structure growth in the KA model. 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 phenomenon. Published by AIP Publishing.

1 aNandi, Ujjwal, Kumar1 aBanerjee, Atreyee1 aChakrabarty, Suman1 aBhattacharyya, Sarika, Maitra uhttp://library.ncl.res.in/content/composition-dependence-glass-forming-ability-binary-mixtures-role-demixing-entropy01640nas a2200169 4500008004100000022001400041245008500055210006900140260000900209300001100218490000800229520104300237100002201280700002501302700003401327856010901361 2017 eng d a0021-960600aFickian yet non-Gaussian behaviour: A dominant role of the intermittent dynamics0 aFickian yet nonGaussian behaviour A dominant role of the intermi cAPR  a1345040 v1463 a

We present a study of the dynamics of small solute particles in a solvent medium where the solute is much smaller in size, mimicking the diffusion of small particles in crowded environment. The solute exhibits Fickian diffusion arising from non-Gaussian Van Hove correlation function. Our study shows that there are at least two possible origins of this non-Gaussian behaviour: the decoupling of the solute-solvent dynamics and the intermittency in the solute motion, the latter playing a dominant role. In the former scenario when averaged over time long enough to explore different solvent environments, the dynamics recovers the Gaussian nature. In the case of intermittent dynamics the non-Gaussianity remains even after long averaging and the Gaussian behaviour is obtained at a much longer time. Our study further shows that only for an intermediate attractive solute-solvent interaction the dynamics of the solute is intermittent. The intermittency disappears for weaker or stronger attractions. Published by AIP Publishing.

1 aAcharya, Sayantan1 aNandi, Ujjwal, Kumar1 aBhattacharyya, Sarika, Maitra uhttp://library.ncl.res.in/content/fickian-yet-non-gaussian-behaviour-dominant-role-intermittent-dynamics00579nas a2200133 4500008004100000245010900041210006900150260000800219490000800227100002200235700002500257700003400282856012900316 2019 eng d00aFickian yet non-Gaussian behaviour: A dominant role of the intermittent dynamics (vol 146, 134504, 2017)0 aFickian yet nonGaussian behaviour A dominant role of the intermi cAUG0 v1511 aAcharya, Sayantan1 aNandi, Ujjwal, Kumar1 aBhattacharyya, Sarika, Maitra uhttp://library.ncl.res.in/content/fickian-yet-non-gaussian-behaviour-dominant-role-intermittent-dynamics-vol-146-134504-201701953nas a2200169 4500008004100000022001400041245004900055210004800104260000800152300001100160490000800171520144900179100002501628700001601653700003401669856008001703 2021 eng d a0021-960600aConnecting real glasses to mean-field models0 aConnecting real glasses to meanfield models cMAR a0945060 v1543 a

We propose a novel model for a glass-forming liquid, which allows us to switch in a continuous manner from a standard three-dimensional liquid to a fully connected mean-field model. This is achieved by introducing k additional particle-particle interactions, which thus augments the effective number of neighbors of each particle. Our computer simulations of this system show that the structure of the liquid does not change with the introduction of these pseudo-neighbors and by means of analytical calculations, and we determine the structural properties related to these additional neighbors. We show that the relaxation dynamics of the system slows down very quickly with the increase in k and that the onset and the mode-coupling temperatures increase. The systems with high values of k follow the mode-coupling theory power law behavior for a larger temperature range compared to the ones with lower values of k. The dynamic susceptibility indicates that the dynamic heterogeneity decreases with the increase in k, whereas the non-Gaussian parameter is independent of it. Thus, we conclude that with the increase in the number of pseudo-neighbors, the system becomes more mean-field-like. By comparing our results with previous studies on mean-field-like systems, we come to the conclusion that the details of how the mean-field limit is approached are important since they can lead to different dynamical behavior in this limit.

1 aNandi, Ujjwal, Kumar1 aKob, Walter1 aBhattacharyya, Sarika, Maitra uhttp://library.ncl.res.in/content/connecting-real-glasses-mean-field-models02090nas a2200181 4500008004100000022001400041245006700055210006700122260000900189300001100198490000800209520150000217100001701717700002401734700002501758700003401783856009101817 2021 eng d a0021-960600aEffective structure of a system with continuous polydispersity0 aEffective structure of a system with continuous polydispersity cJAN  a0345030 v1543 a

In a system of N particles, with continuous size polydispersity, there exists an N(N - 1) number of partial structure factors, making it analytically less tractable. A common practice is to treat the system as an effective one component system, which is known to exhibit an artificial softening of the structure. The aim of this study is to describe the system in terms of M pseudospecies such that we can avoid this artificial softening but, at the same time, have a value of M << N. We use potential energy and pair excess entropy to estimate an optimum number of species, M-0. We then define the maximum width of polydispersity, Delta sigma (0), that can be treated as a monodisperse system. We show that M-0 depends on the degree and type of polydispersity and also on the nature of the interaction potential, whereas Delta sigma (0) weakly depends on the type of polydispersity but shows a stronger dependence on the type of interaction potential. Systems with a softer interaction potential have a higher tolerance with respect to polydispersity. Interestingly, M-0 is independent of system size, making this study more relevant for bigger systems. Our study reveals that even 1% polydispersity cannot be treated as an effective monodisperse system. Thus, while studying the role of polydispersity by using the structure of an effective one component system, care must be taken in decoupling the role of polydispersity from that of the artificial softening of the structure.

1 aPatel, Palak1 aNandi, Manoj, Kumar1 aNandi, Ujjwal, Kumar1 aBhattacharyya, Sarika, Maitra uhttp://library.ncl.res.in/content/effective-structure-system-continuous-polydispersity02480nas a2200241 4500008004100000022001400041245016600055210006900221260000900290300001100299490000800310520158300318100002501901700001701926700001501943700002401958700002501982700002302007700002202030700002202052700003402074856013002108 2022 eng d a0021-960600aThermodynamics and its correlation with dynamics in a mean-field model and pinned systems: a comparative study using two different methods of entropy calculation0 aThermodynamics and its correlation with dynamics in a meanfield  cJAN  a0145030 v1563 aA recent study introduced a novel mean-field model system where each particle over and above the interaction with its regular neighbors interacts with k extra pseudo-neighbors. Here, we present an extensive study of thermodynamics and its correlation with the dynamics of this system. We surprisingly find that the well-known thermodynamic integration (TI) method of calculating the entropy provides unphysical results. It predicts vanishing of the configurational entropy at temperatures close to the onset temperature of the system and negative values of the configurational entropy at lower temperatures. Interestingly, well below the temperature at which the configurational entropy vanishes, both the collective and the single-particle dynamics of the system show complete relaxation. Negative values of the configurational entropy are unphysical, and complete relaxation when the configurational entropy is zero violates the prediction of the random first-order transition theory (RFOT). However, the entropy calculated using the two-phase thermodynamics (2PT) method remains positive at all temperatures for which we can equilibrate the system, and its values are consistent with RFOT predictions. We find that with an increase in k, the difference in the entropy computed using the two methods increases. A similar effect is also observed for a system where a randomly selected fraction of the particles are pinned in their positions in the equilibrated liquid. We show that the difference in entropy calculated via the 2PT and TI methods increases with pinning density.1 aNandi, Ujjwal, Kumar1 aPatel, Palak1 aMoid, Mohd1 aNandi, Manoj, Kumar1 aSengupta, Shiladitya1 aKarmakar, Smarajit1 aMaiti, Prabal, K.1 aDasgupta, Chandan1 aBhattacharyya, Sarika, Maitra uhttp://library.ncl.res.in/content/thermodynamics-and-its-correlation-dynamics-mean-field-model-and-pinned-systems-comparative