Abstract
By a molecular dynamics (MD) simulation method which ensures the system will be under hydrostatic pressure, dynamic and elastic properties of glassy metatstable states are investigated. In the MD method, the simulation cell fluctuates not only in volume but also in shape under constant hydrostatic pressure and temperature. As observed in experiments for many glass forming materials, metastable states in our simulation show a sharp increase in mean-square-displacement at certain temperatures TD. Dynamic heterogeneity is also observed at TD. Elastic properties are calculated from stress and strain relations obtained from the spontaneous fluctuation of internal stress tensor and simulation cell parameters. Each investigated state shows distinctive dynamics while maintaining solid-like elastic properties. The elastic properties stay intact even above TD. It has been shown that the rigidity and mobility of glassy metastable states are compatible under dynamic heterogeneity.
Highlights
Any material can be formed as a glass under the proper experimental conditions [1]
A simple model has an advantage that the knowledge of thermodynamic equilibrium states and phase transitions among them are abundant, making them a preferred reference state for a theoretical description
It is known that constant pressure molecular dynamics (MD) simulations at high pressures lead to sharper phase transitions and the metastable states possess distinct physical properties, for soft spheres [8,9], and for molecules with anisotropic shape [10,11]
Summary
Any material can be formed as a glass under the proper experimental conditions [1]. It is known that constant pressure MD simulations at high pressures lead to sharper phase transitions and the metastable states possess distinct physical properties, for soft spheres [8,9], and for molecules with anisotropic shape [10,11]. It has recently been noticed that residual shear stress exists near inherent structures in constant volume MD simulations as a direct consequence of the imposed boundary [19,20] These studies demonstrate that glassy states are prone to non-hydrostatic stress and more broadly to system size confinement effects.
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