Liquid-liquid phase transition and glass transition in a monoatomic model system

A DPD model of soft spheres with waterlike anomalies and poly(a)morphism

Core-softened approaches have been employed to understand the behavior of a large variety of systems in soft condensed matter, from biological molecules to colloidal crystals, glassy phases, and water-like anomalies. At the same time, dissipative particle dynamics (DPD) is a powerful tool suitable for studying larger length and time scales. In this sense, we propose a simple model of soft molecules that exhibits a wide range of interesting phenomena: polyamorphism, with three amorphous phases, polymorphysm, including a recently found gyroid phase and a cubic diamond structure, reentrant liquid phase, and density, diffusion, and structural water-like anomalies. Each molecule is constituted by two collapsing beads, representing a harder central core and a softer corona. This induces a competition between distinct conformations that leads to their unique behavior. This provides a basis for the development of more accurate water-like DPD models that can then be parameterized for specific systems and even used to model and understand the self-assembly of colloidal crystals.

Stability of the high-density Jagla liquid in 2D: sensitivity to parameterisation

We computed the pressure-temperature phase diagram of the hard-core two-scale ramp potential in two-dimensions, with the parameterisation originally suggested by Jagla [E. A. Jagla, Phys. Rev. E, 63, 061501 (2001)], as well as with a series of systematically modified variants of the model to reveal the sensitivity of the stability of phases. The nested sampling method was used to explore the potential energy landscape, allowing the identification of thermodynamically relevant phases, such as low- and high-density liquids and various crystalline forms, some of which have not been reported before. We also proposed a smooth version of the potential, which is differentiable beyond the hard-core. This potential reproduces the density anomaly, but forms a dodecahedral quasi-crystal structure at high pressure. Our results allow to hypothesise on the necessary modifications of the original model in order to improve the stability of the metastable high-density liquid phase in 3D.

Insight into Liquid Polymorphism from the Complex Phase Behavior of a Simple Model

We systematically explored the phase behavior of the hard-core two-scale ramp model suggested by Jagla [Phys. Rev. E 63, 061501 (2001)PRESCM1539-375510.1103/PhysRevE.63.061501] using a combination of the nested sampling and free energy methods. The sampling revealed that the phase diagram of the Jagla potential is significantly richer than previously anticipated, and we identified a family of new crystalline structures, which is stable over vast regions in the phase diagram. We showed that the new melting line is located at considerably higher temperature than the boundary between the low- and high-density liquid phases, which was previously suggested to lie in a thermodynamically stable region. The newly identified crystalline phases show unexpectedly complex structural features, some of which are shared with the high-pressure ice VI phase.

Modeling the annealing and thermal stability of silver dental amalgam

Effect of heat treatment on the structure and thermal properties of silver-copper dental amalgam (Ag-Cu/Hg) was investigated by means of Monte Carlo (MC) simulation. Simulated pair correlation functions in the framework of MC algorithm form the basis for a diverse analysis of the amalgam annealed up to 2893 K. As heat treatment increases, structural properties remain essentially unchanged up to 1093 K, beyond which, the properties are deteriorated. Phase separation in the context of homo-coordination and segregation of Ag-Cu alloy is characterized as the annealing of amalgam alloy is proceeded. Thus, the amalgam alloy could also maintain a microstructural phase and a structural strength around this temperature, consistent with the annealing reported experimentally. These findings provide insights into amalgam industrial technology, setting amalgamation process, Hg release in dental clinics, and basic information appreciated in the dentistry industry and partnership in forensic science. Graphical abstract Thermal stability of the homogeneous amalgam (Ag-Cu/Hg) is studied up to 2893 K where a phase separation and structural alteration is noted above 1093 and Hg phase segregates into a domain different from Ag-Cu alloy domain.

Structural properties of the Jagla fluid

The structural properties of the Jagla fluid are studied by Monte Carlo (MC) simulations, numerical solutions of integral equation theories, and the (semi-analytical) rational-function approximation (RFA) method. In the latter case, the results are obtained from the assumption (supported by our MC simulations) that the Jagla potential and a potential with a hard core plus an appropriate piecewise constant function lead to practically the same cavity function. The predictions obtained for the radial distribution function, g(r), from this approach are compared against MC simulations and integral equations for the Jagla model, and also for the limiting cases of the triangle-well potential and the ramp potential, with a general good agreement. The analytical form of the RFA in Laplace space allows us to describe the asymptotic behavior of g(r) in a clean way and compare it with MC simulations for representative states with oscillatory or monotonic decay. The RFA predictions for the Fisher-Widom and Widom lines of the Jagla fluid are obtained.

Thermodynamic anomaly of the sub-T(g) relaxation in hyperquenched metallic glasses

Recently, we observed an unusual non-monotonic glass relaxation phenomenon, i.e., the three-step sub-T(g) relaxation in hyperquenched CuZrAl glass ribbons [L. N. Hu and Y. Z. Yue, Appl. Phys. Lett. 98, 081904 (2011)]. In the present work, we reveal the origin of this abnormal behavior by studying the cooling rate dependence of the sub-T(g) enthalpy relaxation in two metallic glasses. For the Cu46Zr46Al8 glass ribbons the sub-T(g) enthalpy relaxation pattern exhibits a three-step trend with the annealing temperature only when the ribbons are fabricated below a critical cooling rate. For the La55Al25Ni20 glass ribbons the activation energy for the onset of the sub-T(g) enthalpy relaxation also varies non-monotonically with the cooling rate of fabrication. These abnormal relaxation phenomena are explained in terms of the competition between the low and the high temperature clusters during the fragile-to-strong transition. By comparisons of chemical heterogeneity between Cu46Zr46Al8 and La55Al25Ni20, we predict that the abnormal relaxation behavior could be a general feature for the HQ metallic glasses.

Core-softened fluids as a model for water and the hydrophobic effect

An interaction model with core-softened potential in three dimensions was studied by Monte Carlo computer simulations and integral equation theory. We investigated the possibility that a fluid with a core-softened potential can reproduce anomalies found experimentally in liquid water, such as the density anomaly, the minimum in the isothermal compressibility as a function of temperature, and others. Critical points of the fluid were also determined. We provided additional arguments that the old notion, postulating that only angular-dependent interactions result in density anomaly, is incorrect. We showed that potential with two characteristic distances is sufficient for the system to exhibit water-like behavior and anomalies, including the famous density maximum. We also found that this model can properly describe the hydrophobic effect.