title: Shear modulus of simulated glass-forming model systems: effects of boundary condition, temperature, and sampling time.
abstract: The shear modulus G of two glass-forming colloidal model systems in d = 3 and d = 2 dimensions is investigated by means of, respectively, molecular dynamics and Monte Carlo simulations. Comparing ensembles where either the shear strain γ or the conjugated (mean) shear stress τ are imposed, we compute G from the respective stress and strain fluctuations as a function of temperature T while keeping a constant normal pressure P. The choice of the ensemble is seen to be highly relevant for the shear stress fluctuations μ(F)(T) which at constant τ decay monotonously with T following the affine shear elasticity μ(A)(T), i.e., a simple two-point correlation function. At variance, non-monotonous behavior with a maximum at the glass transition temperature T(g) is demonstrated for μF(T) at constant γ. The increase of G below T(g) is reasonably fitted for both models by a continuous cusp singularity, G(T) ∝ (1 - T∕T(g))(1∕2), in qualitative agreement with recent theoretical predictions. It is argued, however, that longer sampling times may lead to a sharper transition.
authors.affiliation: Institut Charles Sadron, Université de Strasbourg & CNRS, 23 rue du Loess, 67034 Strasbourg Cedex, France. joachim.wittmer@ics-cnrs.unistra.fr.
authors.forename: J P
authors.initials: JP
authors.lastname: Wittmer
authors.forename: H
authors.initials: H
authors.lastname: Xu
authors.forename: P
authors.initials: P
authors.lastname: Polińska
authors.forename: F
authors.initials: F
authors.lastname: Weysser
authors.forename: J
authors.initials: J
authors.lastname: Baschnagel