Profiles of electrostatic potential across the water-vapor, ice-vapor and ice-water interfaces

Ice-water, water-vapor interfaces and ice surface are studied by molecular dynamics simulations with the SPC/E model of water molecules having the purpose to estimate the profiles of electrostatic potential across the interfaces. We have proposed a methodology for calculating the profiles of electrostatic potential based on a trial particle, which showed good agreement for the case of electrostatic potential profile of the water-vapor interface of TIP4P model calculated in another way. The measured profile of electrostatic potential for the pure ice-water interface decreases towards the liquid bulk region, which is in agreement with simulations of preferential direction of motion of Li$^{+}$ and F$^{-}$ solute ions at the liquid side of the ice-water interface. These results are discussed in connection with the Workman-Reynolds effect.Comment: 7 pages, 5 figure

The effect of stirring on the heterogeneous nucleation of water and of clathrates of tetrahydrofuran/water mixtures

The statistics of liquid-to-crystal nucleation are measured for both water and for clathrate-forming mixtures of tetrahydrofuran (THF) and water using an automatic lag time apparatus (ALTA). We measure the nucleation temperature using this apparatus in which a single sample is repeatedly cooled, nucleated and thawed. The effect of stirring on nucleation has been evaluated numerically and is discussed. We find that stirring of the solution makes no difference to the nucleation temperature of a given solution in a given tube.Comment: 4 pages, 4 figure

How should a small country respond to climate change?

Responses to the global climate crisis often focus on the largest current emitters of greenhouse gases. However, analysis shows that about a third of emissions come from a collection of small emitters, each contributing one- to two-percent of the total additional CO$_2$ injected into the communal atmosphere. Attempts to hold global warming to less than 1.5\textcelsius~ cannot succeed without also reducing emissions from these small countries.Comment: 4 pages, 3 figure

Calculation of the entropy from multiparticle correlation functions

This is the publisher's version, also available electronically from http://journals.aps.org/pra/abstract/10.1103/PhysRevA.45.5680.We consider three approximate expressions for the entropy of a single-particle fluid that require as input only the pair-correlation function g(r). By evaluating numerically these entropy estimates, for several model interparticle interactions of varying range, we examine the accuracy of these expressions compared to the ‘‘exact’’ entropy determined from computer simulation. With the exception of the one-component plasma at very low densities, the entropy of all systems studied can be approximated within 10% of the exact value for fluid densities up to 95% of the freezing density, with the agreement improving for the shorter-ranged potentials. For hard spheres, a preliminary extension to third-order terms is presented

Entropy of electrolytes

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/100/5/10.1063/1.466365The entropy of 1–1 and 2–2 model electrolytes is calculated from an expansion in terms of the multiparticle correlation functions. For electrolytes, a simple truncation of this expansion is never sufficient for the accurate calculation of the entropy,even in the limit of low concentration, in marked contrast to the behavior for short‐ranged potentials. However, a partial, but infinite‐order, summation of the expansion is shown to yield both the correct low‐concentration limit and excellent results over a wide range of concentrations for both 1–1 and 2–2 electrolytes. The consequences of this result for some earlier applications of the entropy expansion to electrolytes are discussed

The crystal–liquid interface of a body‐centered‐cubic‐forming substance: Computer simulations of the r − 6 potential

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/91/6/10.1063/1.456897.The interfaces between a bcc crystal and its melt are studied by molecular dynamics simulation. Three distinct crystal/melt interfaces, (100), (111), and (110) are studied. For all interfaces the variation with z, the coordinate perpendicular to the interfacial plane, of the single particle density (averaged over the directions perpendicular to z) and the diffusion constant are measured. Although the 10–90 widths of the density peak‐height profiles differ significantly among the three interfaces (6, 9, and 7 molecular diameters, respectively), the corresponding 10–90 widths of the diffusion constant profiles are nearly identical with a common value of about four molecular diameters. This leads to the conclusion that the differences in apparent structural width are due primarily to geometric considerations and not to differences in average local molecular environments

Consistent integral equations for two- and three-body-force models: Application to a model of silicon

This is the publisher's version, also available electronically from http://journals.aps.org/pre/abstract/10.1103/PhysRevE.47.2491.Functional differentiation of systematic expansions for the entropy, in the grand ensemble [B. B. Laird and A. D. J. Haymet, Phys. Rev. A 45, 5680 (1992)], leads directly to consistent integral equations for classical systems interacting via two-body, three-body, and even higher-order forces. This method is both a concise method for organizing existing published results and for deriving previously unpublished, higher-order integral equations. The equations are automatically consistent in the sense that all thermodynamic quantities may be derived from a minimum on an approximate free-energy surface, without the need to introduce weighting functions or numerically determined crossover functions. A number of existing approximate theories are recovered by making additional approximations to the equations. For example, the Kirkwood superposition approximation is shown to arise from a particular approximation to the entropy. The lowest-order theory is then used to obtain integral-equation predictions for the well-known Stillinger-Weber model for silicon, with encouraging results. Further connections are made with increasingly popular density-functional methods in classical statistical mechanics

Density functional theory of freezing for hexagonal symmetry: Comparison with Landau theory

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/88/6/10.1063/1.453839.Density functional theory, studied recently by us [J. Chem. Phys. 8 7, 5449 (1987)] is used to study the freezing of hard disks and hard spheres into crystals with hexagonal symmetry. Two different numerical techniques are used, namely a Gaussian approximation to the crystal density and a more general Fourier expansion of the crystal density. The results from these methods are compared with each other, more approximate versions of density functional theory, and computer simulations. In addition, we compare density functional theory with Landau theories of first order transitions, in which the free energy is expanded as a power series, usually in just one order parameter. We find that traditional Landau theory has little validity when applied to the freezing transition

Calculation of the entropy of binary hard sphere mixtures from pair correlation functions

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/97/3/10.1063/1.463103.We evaluate the entropy of several binary hard sphere fluid mixtures using two approximate expressions that require as input only the pair correlation functions,g αβ(r). An approximation based on the incompressible limit is found to be accurate for medium to high density fluids

Density-Functional Theory of Quantum Freezing: Sensitivity to Liquid-State Structure and Statistics

Density-functional theory is applied to compute the ground-state energies of quantum hard-sphere solids. The modified weighted-density approximation is used to map both the Bose and the Fermi solid onto a corresponding uniform Bose liquid, assuming negligible exchange for the Fermi solid. The required liquid-state input data are obtained from a paired phonon analysis and the Feynman approximation, connecting the static structure factor and the linear response function. The Fermi liquid is treated by the Wu-Feenberg cluster expansion, which approximately accounts for the effects of antisymmetry. Liquid-solid transitions for both systems are obtained with no adjustment of input data. Limited quantitative agreement with simulation indicates a need for further improvement of the liquid-state input through practical alternatives to the Feynman approximation.Comment: IOP-TeX, 21 pages + 7 figures, to appear, J. Phys.: Condens. Matte