Coexistence of low and high overlap phases in a supercooled liquid: An integral equation investigation

The pair structure, free energy, and configurational overlap order parameter Q of an annealed system of two weakly coupled replicas of a supercooled \u201csoft sphere\u201d fluid are determined by solving the hypernetted-chain (HNC) and self-consistent Rogers-Young (RY) integral equations over a wide range of thermodynamic conditions \u3c1 (number-density), T (temperature), and inter-replicas couplings \u3b512. Analysis of the resulting effective (or Landau) potential W(\u3c1,T; Q) and of its derivative with respect to Q confirms the existence of a \u201cprecursor transition\u201d between weak and strong overlap phases below a critical temperature Tc well above the temperature To of the \u201cideal glass\u201d transition observed in the limit \u3b512\u21920. The precursor transition is signalled by a loss of convexity of the potential W(Q) and by a concomitant discontinuity of the order parameter Q just below Tc, which crosses over to a mean-field-like van der Waals loop at lower temperatures. The HNC and RY equations lead to the same phase transition scenario, with quantitative differences in the predicted temperatures Tc and To

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Comparison between integral equation method and molecular dynamics simulation for three-body forces: Application to supercritical argon

The prediction of the structural and thermodynamic properties of supercritical argon has been carried out by two independent routes: semianalytical calculations and numerical simulations. The first one is based on the hybridized mean spherical approximation (HMSA) conjugated with an effective pair potential that incorporates multipole dispersion interactions. The second one uses a very recent numerical simulation technique, inspired by the Car–Parrinello method [van der Hoef et al., J. Chem. Phys. 111, 1520 (1999)], which contains an effective quantum-mechanical representation of the underlying electronic structure. The latter approach allows us to treat the contribution of the three-body effects as well, and to validate the use of an effective pair potential for them in the framework of the self-consistent integral equation method. For all the supercritical argon states studied, the results obtained with the semianalytical approach are in good agreement with the predictions of the numerical simulation. Here it is shown that HMSA remains competitive with molecular dynamics simulation when the triple-dipole and the dipole–dipole–quadrupole three-body terms are taken into accoun

Micromachine d'essais mécaniques de type traction et compression ayant une accessibilité optimisée

L'invention concerne une micromachine de traction destinée à être utilisée dans une enceinte de microscope électronique à balayage ou avec un appareil de diffraction, comportant deux mors (1) portés par deux supports, chaque mors (1) étant destiné à recevoir une extrémité d'une éprouvette mécanique (4), et des moyens pour exercer sur les supports des efforts tendant à les écarter l'un de l'autre ou à les rapprocher l'un de l'autre selon une direction longitudinale (AL), chaque mors (1) comprenant une embase (2) et une bride (3) pour fixer une extrémité (21) d'éprouvette (4) au mors (1) en l'enserrant entre la bride (3) et l'embase (2) au moyen d'au moins deux vis (12-15 ) traversant chacune la bride (3) et au moins une partie de l'embase (2), ces deux vis (12-15) étant situées de part et d'autre de l'extrémité d'éprouvette (21)

Micromachine d'essais mécaniques de type traction et compression ayant une accessibilité optimisée

L'invention concerne une micromachine de traction destinée à être utilisée dans une enceinte de microscope électronique à balayage ou avec un appareil de diffraction, comportant deux mors (1) portés par deux supports, chaque mors (1) étant destiné à recevoir une extrémité d'une éprouvette mécanique (4), et des moyens pour exercer sur les supports des efforts tendant à les écarter l'un de l'autre ou à les rapprocher l'un de l'autre selon une direction longitudinale (AL), chaque mors (1) comprenant une embase (2) et une bride (3) pour fixer une extrémité (21) d'éprouvette (4) au mors (1) en l'enserrant entre la bride (3) et l'embase (2) au moyen d'au moins deux vis (12-15 ) traversant chacune la bride (3) et au moins une partie de l'embase (2), ces deux vis (12-15) étant situées de part et d'autre de l'extrémité d'éprouvette (21)

Thermodynamics and dynamics of the hard-sphere system: From stable to metastable states

International audienceA set of three different scaling laws is investigated, which are devoted to link the transport properties, i.e. diffusion coefficient, shear viscosity, bulk viscosity and thermal conductivity, to the thermodynamic properties for the athermal hard-sphere system, over the wider range of packing fraction covering the stable and metastable regimes. Except for the thermal conductivity, the Rosenfeld (1999) [15] relation is found to be applicable to the stable states while the Adam and Gibbs (1965) [24] relation holds well for the metastable states. In contrast, the modified Cohen and Turnbull (1959) [25] relation proposed here gives sound support for a universal scaling law connecting the dynamic and thermodynamic properties, over the domain of packing fraction including the stable and metastable states. In particular, it is found that the most relevant control parameter is not the excess entropy, but the logarithm derivative of the excess entropy with respect to the packing fraction. In the same context, the Stokes-Einstein relation between the diffusion coefficient and the shear viscosity is also examined. The possible violation of the Stokes-Einstein relation is investigated over a large domain of packing fractions

Thermodynamic scaling law for the diffusion coefficient in hard-sphere system

International audienceTwo scaling laws are investigated, which are devoted to link the diffusion coefficient to the thermodynamic properties for the athermal hard-sphere system, over the wide range of packing fraction covering the stable and metastable regimes. It is found that the most relevant control parameter is not the excess entropy, but the compressibility factor, i.e. the logarithm derivative of the excess entropy with respect to the packing fraction

An investigation of the liquid to glass transition using integral equations for the pair structure of coupled replicae

Extensive numerical solutions of the hypernetted-chain (HNC) and Rogers-Young (RY) integral equations are presented for the pair structure of a system of two coupled replicae (1 and 2) of a "soft-sphere" fluid of atoms interacting via an inverse-12 pair potential. In the limit of vanishing inter-replica coupling epsilon(12), both integral equations predict the existence of three branches of solutions: (1) A high temperature liquid branch (L), which extends to a supercooled regime upon cooling when the two replicae are kept at epsilon(12) = 0 throughout; upon separating the configurational and vibrational contributions to the free energy and entropy of the L branch, the Kauzmann temperature is located where the configurational entropy vanishes. (2) Starting with an initial finite coupling epsilon(12), two "glass" branches G(1) and G(2) are found below some critical temperature, which are characterized by a strong remnant spatial inter-replica correlation upon taking the limit epsilon(12) -> 0. Branch G(2) is characterized by an increasing overlap order parameter upon cooling, and may hence be identified with the hypothetical "ideal glass" phase. Branch G(1) exhibits the opposite trend of increasing order parameter upon heating; its free energy lies consistently below that of the L branch and above that of the G(2) branch. The free energies of the L and G(2) branches are found to intersect at an alleged "random first-order transition" (RFOT) characterized by weak discontinuities of the volume and entropy. The Kauzmann and RFOT temperatures predicted by RY differ significantly from their HNC counterparts