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SUMMARY:Role of Pair and Higher Order Correlations in Entropy and Dynamics
  of Glass Forming Systems - Sarika Bhattacharyya\, National Chemical Labor
 atory\, Pune\, India
DTSTART:20150511T131500Z
DTEND:20150511T141500Z
UID:TALK58743@talks.cam.ac.uk
CONTACT:Lucy Colwell
DESCRIPTION:We present a study of two model liquids\, Lennard Jones (LJ) a
 nd its repulsive counter part (WCA)\, exhibiting\nsimilar structure but si
 gnificantly different dynamics at low temperatures [1]. The observation ra
 ises questions\nabout the role of structure and thermodynamics in determin
 ing the dynamics. The well known Adam-Gibbs (AG) relation\, τ(T) = τ_o e
 xp (A/TS_c)\, expresses relaxation times τ in terms of a thermodynamic qu
 antity\, the configurational entropy S_c. By evaluating S_c\, we show that
  the AG relationship quantitatively captures the differences in the dynami
 cs between the LJ and WCA systems thus predicting that the differences in 
 the dynamics of these systems can be understood in terms of their thermody
 namic differences [2]. In order to analyze the independent role of pair an
 d many body correlations we re-express the AG relation in terms of pair co
 nfigurational entropy S_c2 and residual multiparticle entropy\, ∆S\, and
  show that although the pair contribution diverges at higher temperatures 
 reminiscent of the well known mode coupling theory (MCT) behaviour\, they 
 capture the corresponding differences in τ(T) of the two systems [2]. Thu
 s similar structures of the two systems predict different S_c2 values\, in
 dicating a strong sensitivity of the later to changes in the former [2]. H
 owever\, as expected the pair entropy is not enough to explain the correct
  dynamics and the residual multiparticle entropy arising from many body co
 rrelation is essential. But an interesting observation is that the ∆S\, 
 speeds up the dynamics at low temperatures\, which is at odds with the not
 ion that stronger multiparticle correlations are responsible for the stron
 ger temperature dependence of the relaxation times [2]. We further show th
 at the AG theory which is based on activation dynamics can completely desc
 ribe the MCT power law behavior in the region where the latter is found to
  be valid [3]. Since the configurational entropy has a finite value at the
  MCT transition temperature\, T_c\, the AG relation is not expected to pre
 dict any avoided transition in this regime. Our study reveals that althoug
 h Sc is finite\, Sc2 vanishes at T_K2 and in the MCT regime provides a dom
 inant contribution to the total configuratonal entropy. We further find th
 at T_K2 ≃ T_c \, thus concluding that the avoided transition at T_c obse
 rved in the AG relation is due to the vanishing of S_c2 [3].\n\nReferences
 \n[1] L. Berthier and G. Tarjus\, Phys. Rev. Lett. 103\,170601 (2009).\n[2
 ] A. Banerjee\, S. Sengupta\, S. Sastry and S. M. Bhattacharyya \, Phys. R
 ev. Lett. 113\, 225701 (2014).\n[3] M. K. Nandi\, A. Banerjee\, S. Sengupt
 a\, S. Sastry and S. M. Bhattacharyya (to be submitted).
LOCATION:Todd Hamied Room\, Dept. of Chemistry
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