2,792 research outputs found
Water-like Anomalies of Core-Softened Fluids: Dependence on the Trajectories in () Space
In the present article we carry out a molecular dynamics study of the
core-softened system and show that the existence of the water-like anomalies in
this system depends on the trajectory in space along which the
behavior of the system is studied. For example, diffusion and structural
anomalies are visible along isotherms, but disappears along the isochores and
isobars, while density anomaly exists along isochors. We analyze the
applicability of the Rosenfeld entropy scaling relations to this system in the
regions with the water-like anomalies. It is shown that the validity of the of
Rosenfeld scaling relation for the diffusion coefficient also depends on the
trajectory in the space along which the kinetic coefficients and the
excess entropy are calculated.Comment: 10 pages, 10 Fig
Properties of Liquid Iron along the Melting Line up to the Earth-core Pressures
We report a molecular dynamics study of transport coefficients and infinite
frequency shear mod- ulus of liquid iron at high temperatures and high
pressures. We observe a simultaneous rise of both shear viscosity and diffusion
coefficient along the melting line and estimate if liquid iron can vitrify
under Earth-core conditions. We show that in frames of the model studied in our
work iron demonstrates a moderate increase of viscosity along the melting line.
It is also demonstrated that in the limit of high temperatures and high
pressures the liquid iron behaves similar to the soft spheres system with
exponent n=4.6.Comment: 6 pages, 3 figure
Transport coefficients of soft sphere fluids at high densities
Molecular dynamics computer simulation has been used to compute the
self-diffusion coefficient, and shear viscosity of soft-sphere fluids, in which
the particles interact through the soft-sphere or inverse power pair potential.
The calculations have been made along the melting line in a wide range of
pressures and temperatures. The validity of scaling relations for thermodynamic
parameters and kinetic coefficients was checked. It was shown that the
Stokes-Einstein relationship is obeyed if the Barker diameter is used as a
characteristic length scale. It was also shown that the viscosity is
non-monotonic along the isochores as predicted by Ya. Rosenfeld. It was shown
that the viscosity is strongly growing along the melting line, however, this
increase does not stimulate the glass transition because the relaxation time is
decreasing.Comment: 11 pages, 16 figs
A novel anomalous region of water
Water is the most important liquid in the Universe. At the same time it is
the most anomalous liquid. It demonstrates several dozens of anomalies, among
which are density anomaly, diffusion anomaly etc. Anomalous behavior of water
is a topic numerous publications. However, most of the publications investigate
the anomalous behavior of water in the vicinity of critical points: the
liquid-gas critical point and the second hypothetical critical point in
supercooled region. Here we analyze experimental data on such properties of
water as heat capacity, speed of sound, dynamic viscosity and thermal
conductivity. We show that these properties demonstrate anomalous maxima and
minima in a region which is far from both critical points. Therefore, we find a
novel region of anomalous properties of water (anomalous triangle) which cannot
be related to critical fluctuations. We also perform a molecular dynamics
simulations of this region with two common water models - SPC/E and TIP4P - and
show that these models fail to describe the novel anomalous region
Possible phase transition in liquid Cesium at ambient pressure
We report a molecular dynamics study of liquid cesium at ambient pressure
intended to check the possibility of liquid-liquid phase transformation at
K. We find the presence of small kinks on thermodynamic characteristics
of the system, but no phase transition
Dynamical Crossover in Supercritical Water
Dynamical crossover in water is studied by means of computer simulation. The
crossover temperature is calculated from the behavior of velocity
autocorrelation functions. The results are compared with experimental data. It
is shown that the qualitative behavior of the dynamical crossover line is
similar to the melting curve behavior. Importantly, the crossover line belongs
to experimentally achievable region which stimulates the experimental
investigation in this field.Comment: 5 pages, 3 figure
Anomalous behavior of dispersion of longitudinal and transverse collective excitations in water
We study the dependence of the excitation frequency of water along an
isochore and an isotherm crossing the region of density anomaly. We have shown
that the frequency of the longitudinal excitations demonstrated anomalous
dependence on temperature along the isochore. At the same time the dependence
for both longitudinal and transverse excitation frequencies on density along
the isotherm are very modest or even negligible in rather wide range of
densities. This kind of behavior also seems anomalous in comparison with the
ordinary liquids
Silica-Like Sequence of Anomalies in Core-Softened Systems
In this paper we present a simulation study of density, structural and
diffusion anomalies in core-softened system introduced in our previous
publications. It is well-known, that with appropriate parametrization,
core-softened systems are remarkable model liquids that exhibit anomalous
properties observed in tetrahedral liquids such as silica and water. It is
widely believed that core-softened potentials demonstrate the water-like
sequence of anomalies. We show that with increasing the depth of the attractive
part of the potential the order of the region of anomalous diffusion and the
regions of density and structural anomalies is inverted and have the
silica-like sequence. We also show that the slope of the Widom line is negative
like in water.Comment: 5 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1109.164
Water in Asbestos
We present the molecular simulation study of the behavior of water and sodium
chloride solution confined in lizardite asbestos nanotube which is a typical
example of hydrophilic confinement. The local structure, orientational and
dynamic properties are studied. It is shown that the diffusion coefficient
drops about two orders of magnitude comparing to the bulk case, and water in
lizardite asbestos tubes experiences vitrification rather then crystallization
upon cooling in accordance with the results for some other hydrophilic
confinements. The behavior of sodium chloride solutions also considered and the
formation of double layer is observed. It is shower that both sodium and
chlorine have larger diffusion coefficients then water.Comment: 8 pages, 12 figure
The Behavior of Cyclohexane Confined in Slit Carbon Nanopore
It is well known that confining a liquid into a pore strongly alters the
liquid behavior. Investigations of the effect of confinement are of great
importance for many scientific and technological applications. Here we present
a molecular dynamics study of the behavior of cyclohexane confined in carbon
slit pores. The local structure and orientational ordering of cyclohexane
molecules are investigated. It is shown that the system freezes with decreasing
the pore width, and the freezing temperature of nanoconfined cyclohenae is
higher than the bulk one.Comment: 18 pages, 7 figure
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