14 research outputs found
-independent slow-dynamics in atomic and molecular systems
Investigating million-atom systems for very long simulation times, we
demonstrate that the collective density-density correlation time
() in simulated supercooled water and silica becomes wavevector
independent () when the probing wavelength is several times larger than
the interparticle distance. The -independence of the collective
density-density correlation functions, a feature clearly observed in
light-scattering studies of some soft-matter systems, is thus a genuine feature
of many (but not all) slow-dynamics systems, either atomic, molecular or
colloidal. Indeed, we show that when the dynamics of the density fluctuations
is due to particle-type diffusion, as in the case of the Lennard Jones binary
mixture model, the regime does not set in and the relaxation time
continues to scale as even at small .Comment: Includes the supplementary materia
Size dependence of dynamic fluctuations in liquid and supercooled water
We study the evolution of dynamic fluctuations averaged over different space lengths and time scales to characterize spatially and temporally heterogeneous behavior of TIP4P/2005 water in liquid and supercooled states. Analyzing a 250 000 molecules simulated system, we provide evidence of the existence, upon supercooling, of a significant enhancement of spatially localized dynamic fluctuations stemming from regions of correlated mobile molecules. We show that both the magnitude of the departure from the value expected for the system-size dependence of an uncorrelated system and the system size at which such a trivial regime is finally recovered clearly increase upon supercooling. This provides a means to estimate an upper limit to the maximum length scale of influence of the regions of correlated mobile molecules. Notably, such an upper limit grows two orders of magnitude on cooling, reaching a value corresponding to a few thousand molecules at the lowest investigated temperature.Fil: Montes de Oca, Joan Manuel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de QuÃmica del Sur. Universidad Nacional del Sur. Departamento de QuÃmica. Instituto de QuÃmica del Sur; ArgentinaFil: Accordino, Sebastián R.. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de QuÃmica del Sur. Universidad Nacional del Sur. Departamento de QuÃmica. Instituto de QuÃmica del Sur; ArgentinaFil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de QuÃmica del Sur. Universidad Nacional del Sur. Departamento de QuÃmica. Instituto de QuÃmica del Sur; ArgentinaFil: Handle, Philip H.. Universidad de Innsbruck; AustriaFil: Sciortino, Francesco. Università degli studi di Roma "La Sapienza"; Itali
Glass Polymorphism in TIP4P/2005 Water: A Description Based on the Potential Energy Landscape Formalism
The potential energy landscape (PEL) formalism is a statistical mechanical
approach to describe supercooled liquids and glasses. Here we use the PEL
formalism to study the pressure-induced transformations between low-density
amorphous ice (LDA) and high-density amorphous ice (HDA) using computer
simulations of the TIP4P/2005 molecular model of water. We find that the
properties of the PEL sampled by the system during the LDA-HDA transformation
exhibit anomalous behavior. In particular, at conditions where the change in
density during the LDA-HDA transformation is approximately discontinuous,
reminiscent of a first-order phase transition, we find that (i) the inherent
structure (IS) energy, , is a concave function of the volume,
and (ii) the IS pressure, , exhibits a van der Waals-like loop.
In addition, the curvature of the PEL at the IS is anomalous, a non-monotonic
function of . In agreement with previous studies, our work suggests that
conditions (i) and (ii) are necessary (but not sufficient) signatures of the
PEL for the LDA-HDA transformation to be reminiscent of a first-order phase
transition. We also find that one can identify two different regions of the
PEL, one associated to LDA and another to HDA. Our computer simulations are
performed using a wide range of compression/decompression and cooling rates. In
particular, our slowest cooling rate (0.01 K/ns) is within the experimental
rates employed in hyperquenching experiments to produce LDA. Interestingly, the
LDA-HDA transformation pressure that we obtain at K and at different
rates extrapolates remarkably well to the corresponding experimental pressure.Comment: Manuscript and Supplementary Materia
Condensation and Demixing in Solutions of DNA Nanostars and Their Mixtures
We present a numerical/theoretical
approach to efficiently evaluate
the phase diagram of self-assembling DNA nanostars. Combining input
information based on a realistic coarse-grained DNA potential with
the Wertheim association theory, we derive a parameter-free thermodynamic
description of these systems. We apply this method to investigate
the phase behavior of single components and mixtures of DNA nanostars
with different numbers of sticky arms, elucidating the role of the
system functionality and of salt concentration. Specifically, we evaluate
the propensity to demix, the gas–liquid phase boundaries and
the location of the critical points. The predicted critical parameters
compare very well with existing experimental results for the available
compositions. The approach developed here is very general, easily
extensible to other all-DNA systems, and provides guidance for future
experiments