02316nas 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-transition02886nas 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-stokes02356nas 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