02652nas a2200181 4500008004100000022001400041245010500055210006900160260008700229300002700316490000800343520189300351100002502244700002202269700002302291700003402314856012202348 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 uhttps://library.ncl.res.in/content/composition-dependence-glass-forming-ability-binary-mixtures-role-demixing-entropy02316nas a2200265 4500008004100000022001400041245008000055210006900135260000800204300001100212490000900223520150000232653001001732653000901742653002301751653002001774653002501794653001201819653002001831100001901851700002401870700002201894700003401916856010001950 2019 eng d a1742-546800aComparative study of a class of mean field theories of the glass transition0 aComparative study of a class of mean field theories of the glass cAUG a0840080 v20193 a

In a recently developed microscopic mean field theory, we have shown that the dynamics of a system, when described only in terms of its pair structure, can predict the correct dynamical transition temperature. Further, the theory predicted the difference in dynamics of two systems (the Lennard-Jones and the Weeks-Chandler-Andersen) despite them having quite similar structures. This is in contrast to the Schweizer-Saltzman (SS) formalism which predicted the dynamics of these two systems to be similar. The two theories although similar in spirit have certain differences. Here we present a comparative study of these two formalism to find the origin of the difference in their predictive power. We show that not only the dynamics in the potential energy surface, as described by our earlier study, but also that in the free energy surface, like in the SS theory, can predict the correct dynamical transition temperature. Even an approximate one component version of our theory, similar to the system used in the SS theory, can predict the transition temperature reasonably well. Interestingly, we show here that despite the above mentioned shortcomings the SS theory can actually predict the correct transition temperatures. Thus microscopic mean field theories of this class which express dynamics in terms of the pair structure of the liquid while being unable to predict the actual dynamics of the system are successful in predicting the correct dynamical transition temperature.

10aaging10aetc)10aglasses (colloidal10aglassy dynamics10amode coupling theory10aPolymer10aslow relaxation1 aSaha, Indranil1 aNandi, Manoj, Kumar1 aDasgupta, Chandan1 aBhattacharyya, Sarika, Maitra uhttps://library.ncl.res.in/content/comparative-study-class-mean-field-theories-glass-transition01923nas a2200169 4500008004100000022001400041245010000055210006900155260000800224300001600232490000800248520129300256100002201549700002201571700003401593856012601627 2019 eng d a1520-610600aComparative study of anomalous size dependence of charged and neutral solute diffusion in water0 aComparative study of anomalous size dependence of charged and ne cDEC a10275-102850 v1233 a

We present a comparative study of size dependence of diffusion for charged and neutral solutes in water. Although both show nonmonotonicity of the size dependence of diffusion, their nature and origin are quite different. For neutral solutes, the peak position and the value of diffusion at the maximum are both independent of the solute water interaction. Interestingly, for charged solutes, with an increase in solute water interaction strength, the peak position shifts to lower solute sizes and with an increase in charge, it shifts to higher solute sizes. The diffusion value at the peak reduces with an increase in both solute water interaction and solute charge. We show that all these features observed for charged solutes can be understood in terms of the interplay between ionic and nonionic interactions which is definitely absent for neutral solutes. Some of the earlier studies addressing the nonmonotonicity in diffusion did suggest the interplay between the two interactions to be the cause. However, this is the first time we show that such an interplay gives rise to the nonmonotonicity in the potential energy which is a prerequisite for obtaining the nonmonotonicity in the diffusion. Such nonmonotonicity in the potential energy is absent for neutral solutes.

1 aAcharya, Sayantan1 aNandi, Ujjwal, K.1 aBhattacharyya, Sarika, Maitra uhttps://library.ncl.res.in/content/comparative-study-anomalous-size-dependence-charged-and-neutral-solute-diffusion-water02886nas a2200193 4500008004100000022001400041245012500055210006900180260000800249300001100257490000700268520214500275653003202420653002502452653003002477100002402507700003402531856012702565 2020 eng d a0953-898400aContinuous time random walk concepts applied to extended mode coupling theory: a study of the Stokes? Einstein breakdown0 aContinuous time random walk concepts applied to extended mode co cFEB a0640010 v323 a

In an attempt to extend the mode coupling theory (MCT) to lower temperatures, some years back an Unified theory was proposed which within the MCT framework incorporated the activated dynamics via the random first order transition theory (RFOT). The theory successfully showed that there is hopping induced diffusive dynamics and the modified MCT coupled to the activated motion continues till low temperatures. Here we show that the theory although successful in describing other properties of supercooled liquids is unable to capture the Stokes?Einstein breakdown. We then show using continuous time random work (CTRW) formalism that the Unified theory is equivalent to a CTRW dynamics in presence of two waiting time distributions. It is known from earlier work on CTRW that in such cases the total dynamics is dominated by the fast motion. This explains the failure of the Unified theory in predicting the SE breakdown as both the structural relaxation and the diffusion process are described by the comparatively fast MCT like dynamics. The study also predicts that other forms of extended MCT with Markovian hopping kernel will face a similar issue. We next modify the Unified theory by applying the concept of renewal theory, usually used in CTRW models where the distribution has a long tail. According to this theory the first jump given by the persistent time is slower than the subsequent jumps given by the exchange time. We first show that for systems with two waiting time distributions even when both the distributions are exponential the persistent time is larger than the exchange time. We also identify the persistent time with the slower activated process. The extended Unified theory can now explain the SE breakdown. In this extended theory at low temperatures the structural relaxation is described by the activated dynamics whereas the diffusion is primarily determined by the MCT like dynamics leading to a decoupling between them. We also calculate a dynamic lengthscale from the wavenumber dependence of the relaxation time. We find that this dynamic length scale grows faster than the static length scale.

10acontinuous time random walk10amode coupling theory10aStokes?Einstein breakdown1 aNandi, Manoj, Kumar1 aBhattacharyya, Sarika, Maitra uhttps://library.ncl.res.in/content/continuous-time-random-walk-concepts-applied-extended-mode-coupling-theory-study-stokes01954nas a2200169 4500008004100000022001400041245004900055210004800104260000800152300001100160490000800171520144900179100002501628700001601653700003401669856008101703 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 uhttps://library.ncl.res.in/content/connecting-real-glasses-mean-field-models02356nas a2200157 4500008004100000022001400041245014500055210006900200260000900269490000800278520170500286100001801991700002402009700003402033856013102067 2023 eng d a0021-960600a Comparative study of the correlation between the structure and the dynamics for systems interacting via attractive and repulsive potentials0 aComparative study of the correlation between the structure and t cSEP 0 v1593 a

We present the study of the structure-dynamics correlation for systems interacting via attractive Lennard-Jones (LJ) and its repulsive counterpart, the Weeks-Chandler-Andersen (WCA) potentials. The structural order parameter (SOP) is related to the microscopic mean-field caging potential. At a particle level, the SOP shows a distribution. Although the two systems have similar pair structures, their average SOP differs. However, this difference alone is insufficient to explain the well known slowing down of the dynamics in the LJ system at low temperatures. The slowing down can be explained in terms of a stronger coupling between the SOP and the dynamics. To understand the origin of this system specific coupling, we study the difference in the microscopic structure between the hard and soft particles. We find that for the LJ system, the structural differences of the hard and soft particles are more significant and have a much stronger temperature dependence compared to the WCA system. Thus, the study suggests that attractive interaction creates more structurally different communities. This broader difference in the structural communities is probably responsible for stronger coupling between the structure and dynamics. Thus, the system specific structure-dynamics correlation, which also leads to a faster slowing down in the dynamics, appears to have a structural origin. A comparison of the predictive power of our SOP with the local energy and two body excess entropy in determining the dynamics shows that in the LJ system, the enthalpy plays a dominant role and in the WCA system, the entropy plays a dominant role, and our SOP can capture both these contributions.

1 aSharma, Mohit1 aNandi, Manoj, Kumar1 aBhattacharyya, Sarika, Maitra uhttps://library.ncl.res.in/content/comparative-study-correlation-between-structure-and-dynamics-systems-interacting-attractive