8,746 research outputs found
Lattice-Boltzmann Model of Amphiphilic Systems
A lattice-Boltzmann model for the study of the dynamics of
oil-water-surfactant mixtures is constructed. The model, which is based on a
Ginzburg-Landau theory of amphiphilic systems with a single, scalar order
parameter, is then used to calculate the spectrum of undulation modes of an
oil-water interface and the spontaneous emulsification of oil and water after a
quench from two-phase coexistence into the lamellar phase. A comparison with
some analytical results shows that the model provides an accurate description
of the static and dynamic behavior of amphiphilic systems.Comment: 6 pages, 2 figures, europhysics-letter styl
Resummed Green-Kubo relations for a fluctuating fluid-particle model
A recently introduced stochastic model for fluid flow can be made Galilean
invariant by introducing a random shift of the computational grid before
collisions. This grid shifting procedure accelerates momentum transfer between
cells and leads to a collisional contribution to transport coefficients. By
resumming the Green-Kubo relations derived in a previous paper, it is shown
that this collisional contribution to the transport coefficients can be
determined exactly. The resummed Green-Kubo relations also show that there are
no mixed kinetic-collisional contributions to the transport coefficients. The
leading correlation corrections to the transport coefficients are discussed,
and explicit expressions for the transport coefficients are presented and
compared with simulation data.Comment: 4 pages including 4 figures, submitted to PRE Rapid Com
Electronic structure and Fermi surface tolopogy of NaCoO
We construct an effective Hamiltonian for the motion of T2g highly correlated
states in NaxCoO2. We solve exactly a multiband model in a CoO6 cluster with
electronic occupation corresponding to a nominal Co valence of either +3 or +4.
Using the ensuing ground states, we calculate the effective O mediated hopping
t=0.10 eV between many-body T2g states, and estimate the direct hopping t'~0.04
eV. The trigonal splitting 3D=0.315 eV is taken from recent quantum chemistry
calculations. The resulting effective Hamiltonian is solved using a generalized
slave-boson mean-field approximation. The results show a significant band
renormalization and a Fermi surface topology that agrees with experiment, in
contrast to predictions using the local-density approximation.Comment: 4 pages, 2 figure
Comparison of weighted-density-functional theories for inhomogeneous liquids
This is the publisher's version, also available electronically from http://journals.aps.org/pra/abstract/10.1103/PhysRevA.42.4806.Three recent weighted-density-functional (WDF) theories are critically examined in terms of their ability to describe correctly the structure of a hard-sphere fluid at a hard wall. A new derivation of the Curtin-Ashcroft WDF theory is given that clarifies the basic approximations behind this formulation and brings out the close relationship between their work and the WDF theories of Meister-Kroll and Groot–van der Eerden. The condition that the second functional derivative of the approximate Helmholtz free-energy functional yields the correct two-particle direct-correlation function in the homogeneous limit is found to be of crucial importance in determining good liquid structures
Freezing of soft spheres: A critical test for weighted-density-functional theories
This is the publisher's version, also available electronically from http://journals.aps.org/pra/abstract/10.1103/PhysRevA.42.4810We study the freezing properties of systems with inverse-power and Yukawa interactions (soft spheres), using recently developed weighted-density-functional theories. We find that the modified weighted-density-functional approximation (MWDA) of Denton and Ashcroft yields results for the liquid to face-centered-cubic (fcc) structure transition that represent a significant improvement over those of earlier ‘‘second-order’’ density-functional freezing theories; however, this theory, like the earlier ones, fails to predict any liquid to body-centered-cubic (bcc) transition, even under conditions where the computer simulations indicate that this should be the equilibrium solid structure. In addition, we show that both the modified effective-liquid approximation (MELA) of Baus [J. Phys. Condens. Matter 2, 2111 (1990)] and the generalized effective-liquid approximation of Lutsko and Baus [Phys. Rev. Lett. 64, 761 (1990)], while giving excellent results for the freezing of hard spheres, fail completely to predict freezing into either fcc or bcc solid phases for soft inverse-power potentials. We also give an alternate derivation of the MWDA that makes clearer its connection to earlier theories
Swelling of particle-encapsulating random manifolds
We study the statistical mechanics of a closed random manifold of fixed area
and fluctuating volume, encapsulating a fixed number of noninteracting
particles. Scaling analysis yields a unified description of such swollen
manifolds, according to which the mean volume gradually increases with particle
number, following a single scaling law. This is markedly different from the
swelling under fixed pressure difference, where certain models exhibit
criticality. We thereby indicate when the swelling due to encapsulated
particles is thermodynamically inequivalent to that caused by fixed pressure.
The general predictions are supported by Monte Carlo simulations of two
particle-encapsulating model systems -- a two-dimensional self-avoiding ring
and a three-dimensional self-avoiding fluid vesicle. In the former the
particle-induced swelling is thermodynamically equivalent to the
pressure-induced one whereas in the latter it is not.Comment: 8 pages, 6 figure
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