Dynamics and configurational entropy in the Lewis-Wahnström model for supercooled orthoterphenyl

Mossa, Stefano; Nave, E. La; Stanley, H. Eugene; Donati, Claudio; Sciortino, Francesco; Tartaglia, P.

doi:10.1103/physreve.65.041205

Cited by 115 publications

(216 citation statements)

References 78 publications

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“…The predicted 1/T dependence of E IS and the parabolic dependence of S conf has been confirmed in several models for fragile liquids [14,17,47]. From the relations above and fits of the numerical data, one obtains: i) the vibrational coefficients a, b and c from Eq.…”

Section: Background: the Gaussian Landscapesupporting

confidence: 54%

“…Hard spheres, soft spheres, Lennard Jones mixtures and simple molecular liquids [10,11,12,13,14,15,16,17] have been extensively studied. Within the potential energy landscape (PEL) [18] thermodynamic approach, detailed comparisons between numerical data and theoretical predictions have been performed.…”

Section: Introductionmentioning

confidence: 99%

“…Within the potential energy landscape (PEL) [18] thermodynamic approach, detailed comparisons between numerical data and theoretical predictions have been performed. Estimates of the number Ω of local minima -basins-as a function of the basin depth and of their shape have been recently evaluated for a few models [11,12,14,15,17,19,20,21,22] and from the analysis of experimental data [23,24,25]. The PEL approach, which is particularly well suited for describing supercooled liquids, provides a controlled way to extrapolate the thermodynamic properties of the liquid state below the lowest temperature at which equilibrated data can be collected.…”

Section: Introductionmentioning

confidence: 99%

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Liquid stability in a model for ortho-terphenyl

Nave

Mossa

Sciortino

et al. 2004

The Journal of Chemical Physics

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We report an extensive study of the phase diagram of a simple model for ortho-terphenyl, focusing on the limits of stability of the liquid state. Reported data extend previous studies of the same model to both lower and higher densities and to higher temperatures. We estimate the location of the homogeneous liquid-gas nucleation line and of the spinodal locus. Within the potential energy landscape formalism, we calculate the distributions of depth, number, and shape of the potential energy minima and show that the statistical properties of the landscape are consistent with a Gaussian distribution of minima over a wide range of volumes. We report the volume dependence of the parameters entering in the Gaussian distribution (amplitude, average energy, variance). We finally evaluate the locus where the configurational entropy vanishes, the so-called Kauzmann line, and discuss the relative location of the spinodal and Kauzmann loci.

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Section: Background: the Gaussian Landscapesupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Liquid stability in a model for ortho-terphenyl

Nave

Mossa

Sciortino

et al. 2004

The Journal of Chemical Physics

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“…However, we note that in three dimensions, the AG relation has been verified in both attractive models (e.g. Kob-Andersen [15], Lewis-Wahnström OTP [16] and Dzugutov liquid [40]) and repulsive models (e.g. repulsive soft spheres [41]).…”

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confidence: 64%

Adam-Gibbs Relation for Glass-Forming Liquids in Two, Three, and Four Dimensions

et al. 2012

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The Adam-Gibbs relation between relaxation times and the configurational entropy has been tested extensively for glass formers using experimental data and computer simulation results. Although the form of the relation contains no dependence on the spatial dimensionality in the original formulation, subsequent derivations of the Adam-Gibbs relation allow for such a possibility. We test the Adam-Gibbs relation in 2, 3, and 4 spatial dimensions using computer simulations of model glass formers. We find that the relation is valid in 3 and 4 dimensions. But in 2 dimensions, the relation does not hold, and interestingly, no single alternate relation describes the results for the different model systems we study.A central theme in the study of glass forming liquids is a satisfactory understanding of the behaviour of relaxation times as the glass transition is approached, showing temperature dependence typically stronger than the Arrhenius law:, which is of central importance in glass forming liquids, explains the behaviour of the relaxation time i.e. dynamics in terms of the configurational entropy i.e. thermodynamics. It also forms the basis of more sophisticated theories of glass transition connecting dynamics to thermodynamics e.g. the random first order transition theory (RFOT) [5][6][7][8][9]. In these theories the spatial dimensionality (D) appears explicitly in the relationship between dynamics and thermodynamics. However, the large number of experimental and numerical studies wherein the AG relation has been tested [10][11][12][13][14][15][16][17] have all been in 3 dimensions. The present study aims to critically examine whether the AG relation is valid in different spatial dimensions or gets generalized in a D dependent way.The AG relation is based on the picture that relaxation in glass forming liquids occurs through the collective rearrangement of "cooperatively rearranging regions" (CRR). The CRRs define a minimum size of groups of rearranging particles (atoms, molecules etc. depending on the nature of the glass former) such that smaller groups of particles are incapable of rearrangement independently of their surroundings. Adam and Gibbs argued that the configurational entropy (the entropy associated with the multiplicity of distinct arrangements of particles, obtained by subtracting a "vibrational" component from the total entropy) per particle S c (T ) of a liquid varies inversely as the size of the CRR, z(T ), since the configurational entropy per CRR, S * , is roughly independent of temperature: S c (T ) = S * z(T ) . The further assumption that the free energy barrier for a rearrangement is proportional to the size of the CRR (∆G = zδµ, δµ = chemical potential barrier per particle) results in the Adam-Gibbs relation:The above relation is obtained independent of reference to the spatial dimensionality of the system and is hence expected to be same in all spatial dimensions. A rationalization of the AG relation, based on more detailed considerations of possible activated relaxation mechanisms, is offer...

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“…Simulation details are given in Refs. [14,15]. The system has been studied in isobaric-isothermal conditions; the time constants of both the thermostat and the barostat have been fixed to 20 ps.…”

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confidence: 99%

Crossover (or Kovacs) Effect in an Aging Molecular Liquid

2004

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We study by means of molecular dynamics simulations the aging behavior of a molecular model of ortho-terphenyl. We find evidence of a a non-monotonic evolution of the volume during an isothermal-isobaric equilibration process, a phenomenon known in polymeric systems as cross-over (or Kovacs) effect. We characterize this phenomenology in terms of landscape properties, providing evidence that, far from equilibrium, the system explores region of the potential energy landscape distinct from the one explored in thermal equilibrium. We discuss the relevance of our findings for the present understanding of the thermodynamics of the glass state.If two systems in thermodynamical equilibrium with identical chemical composition have the same temperature T and volume V we immediately know that they experience the same pressure P . We know that the two systems will respond in the same way to an external perturbation, and that they will be characterized by the same structural and dynamical properties. The ability to predict the pressure, and the equivalence of structural and dynamical properties, derive from thermodynamical principles.In the case of glasses, systems in out-of-equilibrium conditions, the T and V values are not sufficient for predicting P , since the state of the system depends on its previous thermal and mechanical history. Different glasses, at the same T and V , are characterized by different P values. One can ask if the value of P is sufficient to uniquely define the glass state, i.e., if two glasses with identical composition having not only the same T and V but also the same P are the same glass. If this is the case, the two glasses should respond to an external perturbation in the same way and should age with a similar dynamics.These basic questions are at the hearth of a thermodynamic understanding of the glassy state of matter, and of the possibility of providing a theoretical understanding of out-of-equilibrium systems. Indeed, if by specifying T , V and also P , we uniquely define the glass state -its structural and dynamical properties-it means that it is possible to develop an out-of-equilibrium thermodynamic formalism [1,2,3,4,5,6] where the previous history of the system is encoded in one additional parameter. In the interpretation of experimental data, such additional parameter is often chosen as a fictive temperature or pressure, in the attempt to associate the glass to a liquid, frozen from a specific thermodynamic state.Back in the 60th, Kovacs and co-workers designed an experimental protocol [7,8,9] (Fig. 1) to generate distinct glasses with different thermal and mechanical histories but with the same T , V and P values. Poly-vinyl acetate was equilibrated at high temperature T h and then quenched at low temperature T l , where it was allowed to relax isothermally for a waiting time t w insufficient to reach equilibrium. The material was then re-heated to an intermediate temperature T , and allowed to relax. The entire experiment was performed at constant pressure P . The observed dynamics o...

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Dynamics and configurational entropy in the Lewis-Wahnström model for supercooled orthoterphenyl

Cited by 115 publications

References 78 publications

Liquid stability in a model for ortho-terphenyl

Liquid stability in a model for ortho-terphenyl

Adam-Gibbs Relation for Glass-Forming Liquids in Two, Three, and Four Dimensions

Crossover (or Kovacs) Effect in an Aging Molecular Liquid

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