Interplay between structure and density anomaly for an isotropic core-softened ramp-like potential

Using molecular dynamics simulations and integral equations we investigate the structure, the thermodynamics and the dynamics of a system of particles interacting through a continuous core- softened ramp-like interparticle potential. We found density, dynamic and structural anomalies similar to that found in water. Analysis of the radial distribution function for several temperatures at fixed densities show a pattern that may be related to the origin of density anomaly.Comment: 7 pages, 3 figure

A Framework for the Design and Implementation of Learning Objects: a Competence-based Approach

This paper presents a framework for the design and implementation of learning objects using a competence-based approach. This framework is illustrated by the development of a standalone Windows application (Trilho GOA) whose primary purpose is to create standardized pedagogical contents trough the aggregation and standardization of instructional resources in several formats that can be used later on a Learning Management System (LMS) supporting SCORM 1.2. The paper contains a brief introduction to the developed software, its system architecture, main features and several pedagogical advantages for its users

Structural anomalies for a three dimensional isotropic core-softened potential

Using molecular dynamics simulations we investigate the structure of a system of particles interacting through a continuous core-softened interparticle potential. We found for the translational order parameter, t, a local maximum at a density $\rho_{t-max}$ and a local minimum at $\rho_{t-min} > \rho_{t-max}$. Between $\rho_{t-max}$ and $\rho_{t-min}$, the $t$ parameter anomalously decreases upon pressure. For the orientational order parameter, $Q_6$, was observed a maximum at a density $\rho_{t-max}< \rho_{Qmax} < \rho_{t-min}$. For densities between $\rho_{Qmax}$ and $\rho_{t-min}$, both the translational (t) and orientational ($Q_6$) order parameters have anomalous behavior. We know that this system also exhibits density and diffusion anomaly. We found that the region in the pressure-temperature phase-diagram of the structural anomaly englobes the region of the diffusion anomaly that is larger than the region limited by the temperature of maximum density. This cascade of anomalies (structural, dynamic and thermodynamic) for our model has the same hierarchy of that one observed for the SPC/E water.Comment: 19 pages, 8 figure

C−\mathcal {C}-IBI: Targeting cumulative coordination within an iterative protocol to derive coarse-grained models of (multi-component) complex fluids

We present a coarse-graining strategy that we test for aqueous mixtures. The method uses pair-wise cumulative coordination as a target function within an iterative Boltzmann inversion (IBI) like protocol. We name this method coordination iterative Boltzmann inversion ($\mathcal {C}-$IBI). While the underlying coarse-grained model is still structure based and, thus, preserves pair-wise solution structure, our method also reproduces solvation thermodynamics of binary and/or ternary mixtures. Additionally, we observe much faster convergence within $\mathcal {C}-$IBI compared to IBI. To validate the robustness, we apply $\mathcal {C}-$IBI to study test cases of solvation thermodynamics of aqueous urea and a triglycine solvation in aqueous urea

Water-like hierarchy of anomalies in a continuous spherical shouldered potential

We investigate by molecular dynamics simulations a continuous isotropic core-softened potential with attractive well in three dimensions, introduced by Franzese [cond-mat/0703681, to appear on Journal of Molecular Liquids], that displays liquid-liquid coexistence with a critical point and water-like density anomaly. Here we find diffusion and structural anomalies. These anomalies occur with the same hierarchy that characterizes water. Yet our analysis shows differences with respect to the water case. Therefore, many of the anomalous features of water could be present in isotropic systems with soft-core attractive potentials, such as colloids or liquid metals, consistent with recent experiments showing polyamorphism in metallic glasses.Comment: 27 pages, 9 figures. to appear in J. Chem. Phy

An ubiquitous mechanism for waterlike anomalies

Using collision driven molecular dynamics a system of spherical particles interacting through an effective two length scales potential is studied. The potential can be tuned by means of a single parameter, $\lambda$, from a ramp $(\lambda=0.5)$ to a square-shoulder potential $(\lambda=1.0)$ representing a family of two length scales potential in which the shortest interaction distance has higher potential energy than the largest interaction distance. For all the potentials, ranging between the ramp and the square-shoulder, density and structural anomalies were found, while the diffusion anomaly is found in all but in the square-shoulder potential. The presence anomalies in square-shoulder potential, not observed in previous simulations, confirm the assumption that the two length scales potential is an ubiquitous ingredient for a system to exhibit water-like anomaliesComment: 6 pages, 7 figure

Liquid crystal phase and waterlike anomalies in a core-softened shoulder-dumbbells system

Using molecular dynamics we investigate the thermodynamics, dynamics and structure of 250 diatomic molecules interacting by a core-softened potential. This system exhibits thermodynamics, dynamics and structural anomalies: a maximum in density-temperature plane at constante pressure and maximum and minimum points in the diffusivity and translational order parameter against density at constant temperature. Starting with very dense systems and decreasing density the mobility at low temperatures first increases, reach a maximum, then decreases, reach a minimum and finally increases. In the pressure-temperature phase diagram the line of maximum translational order parameter is located outside the line of diffusivity extrema that is enclosing the temperature of maximum density line. We compare our results with the monomeric system showing that the anisotropy due to the dumbbell leads to a much larger solid phase and to the appearance of a liquid crystal phase. the double ranged thermodynamic and dynamic anomalies.Comment: 14 pages, 5 figure

Thermodynamic and dynamic anomalies for a three dimensional isotropic core-softened potential

Using molecular dynamics simulations and integral equations (Rogers-Young, Percus-Yevick and hypernetted chain closures) we investigate the thermodynamic of particles interacting with continuous core-softened intermolecular potential. Dynamic properties are also analyzed by the simulations. We show that, for a chosen shape of the potential, the density, at constant pressure, has a maximum for a certain temperature. The line of temperatures of maximum density (TMD) was determined in the pressure-temperature phase diagram. Similarly the diffusion constant at a constant temperature, $D$, has a maximum at a density $\rho_{max}$ and a minimum at a density $\rho_{min}<\rho_{max}$. In the pressure-temperature phase-diagram the line of extrema in diffusivity is outside of TMD line. Although in this interparticle potential lacks directionality, this is the same behavior observed in SPC/E water.Comment: 16 page