26 research outputs found
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
Thermodynamic and Dynamic Anomalies for Dumbbell Molecules Interacting with a Repulsive Ramp-Like Potential
Using collision driven discrete molecular dynamics (DMD), we investigate the
thermodynamics and dynamics of systems of 500 dumbbell molecules interacting by
a purely repulsive ramp-like discretized potential, consisting of steps of
equal size. We compare the behavior of the two systems, with and steps. Each system exhibits both thermodynamic and dynamic anomalies, a
density maximum and the translational and rotational mobilities show anomalous
behavior. Starting with very dense systems and decreasing the density, both
mobilities first increase, reache a maximum, then decrease, reache a minimum,
and finally increase; this behavior is similar to the behavior of SPC/E water.
The regions in the pressure-temperature plane of translational and rotational
mobility anomalies depend strongly on . The product of the translational
diffusion coefficient and the orientational correlation time increases with
temperature, in contrast with the behavior of most liquids
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 and a local minimum at . Between and , the parameter
anomalously decreases upon pressure. For the orientational order parameter,
, was observed a maximum at a density . For densities between and , both the
translational (t) and orientational () 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
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
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 (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 IBI compared to IBI. To validate the
robustness, we apply IBI to study test cases of solvation
thermodynamics of aqueous urea and a triglycine solvation in aqueous urea
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, , has a maximum
at a density and a minimum at a density .
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