The electronic properties of inversion and accumulation layers at semiconductor-insulator interfaces and of other systems that exhibit two-dimensional or quasi-two-dimensional behavior, such as electrons in semiconductor heterojunctions and superlattices and on liquid helium, are reviewed. Energy levels, transport properties, and optical properties are considered in some detail, especially for electrons at the (100) silicon-silicon dioxide interface. Other systems are discussed more briefly.

Electronic properties of two-dimensional systems

We study a class of photonic crystals in which both the dielectric constant e d the magnetic permeability m vary within the crystal. We find that in the case where both e andm have their maximum values in the same material, the photonic band gaps tend to disappear. However, in the opposite case where e andm have their maximum values in different materials, the gaps become wider with maximum gap over midgap frequency as high as 0.8. We also discuss the possibility of designing such photonic crystals with ferrites. @S0163-1829 ~97!06227-9# BRIEF REPORTS

Physical Review B

We review the current state of knowledge of phase separation and phase equilibria in porous materials. Our emphasis is on fundamental studies of simple fluids (composed of small, neutral molecules) and well-characterized materials. While theoretical and molecular simulation studies are stressed, we also survey experimental investigations that are fundamental in nature. Following a brief survey of the most useful theoretical and simulation methods, we describe the nature of gas‐liquid (capillary condensation), layering, liquid‐liquid and freezing/melting transitions. In each case studies for simple pore geometries, and also more complex ones where available, are discussed. While a reasonably good understanding is available for phase equilibria of pure adsorbates in simple pore geometries, there is a need to extend the models to more complex pore geometries that include effects of chemical and geometrical heterogeneity and connectivity. In addition, with the exception of liquid‐liquid equilibria, little work has been done so far on phase separation for mixtures in porous media.

/pdf/phase-separation-in-confined-systems-4y1g4brne6.pdf

Phase separation in confined systems

Classical and degenerate, strongly coupled plasmas are approached by computer simulations, analytic theories, and variational methods. Thermodynamic properties predicted in those various approaches are compared and examined; possibilities of Wigner crystallization and other instabilities are investigated. Salient features in the static and dynamic correlations are reviewed. Screening effects are analyzed and applied to calculations of the enhancement factor of the thermonuclear reaction rate and the electric resistivity in dense plasmas. Theoretical predictions on the dynamic properties are compared with the x ray and electron scattering data for the metallic electrons.

Strongly coupled plasmas: high-density classical plasmas and degenerate electron liquids

Several methods are available for calculating shear viscosities of liquids from molecular dynamics simulations. There are equilibrium methods based on pressure or momentum fluctuations and several nonequilibrium methods. For the nonequilibrium method using a periodic shear flow, all relevant quantities, including the accuracy, can be estimated before performing the simulation. We compared the applicability, accuracy and efficiency of this method with two equilibrium methods and another nonequilibrium method, using simulations of a Lennard-Jones fluid and the SPC and SPC/E [(extended) simple point charge] water models.

/pdf/determining-the-shear-viscosity-of-model-liquids-from-nu3bmy7e8x.pdf

Determining the shear viscosity of model liquids from molecular dynamics simulations

A theory of electron correlations based on a generalized random-phase approximation is presented An expression for the local-field correction is obtained using the third frequency moment of the spectral function of the electron-density response function The local field is a functional of the structure factor $S(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ which in turn is related to the imaginary part of the dielectric function via the fluctuation-dissipation theorem The equations are self-consistently solved to determined $S(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ as originally suggested by Singwi et al The pair-correlation function, compressibility, plasma dispersion, and correlation energy of electron liquid at metallic densities have been calculated

Electron correlations and moment sum rules

The sixth frequency moment of the spectral functions of both the longitudinal and transverse current correlations along with their self-parts has been derived for a system of particles interacting through a two-body potential. The first two frequency moments of the spectral function of the energy-density fluctuation, and the first four frequency moments of the spectral function of the kinetic-energy-density fluctuation-correlation functions have also been derived. Numerical estimates for the fourth and sixth frequency moments of the spectral function of the longitudinal current correlations have been made for liquid argon. From this some information about the behavior of the contributions of triplet and quadruplet correlation functions to the frequency moments of liquid argon have been obtained. Numerical estimates have also been made for the first four frequency moments of the kinetic-energy-density fluctuation-correlation function in the long-wavelength limit for liquid argon.

Sum rules and atomic correlations in classical liquids

In this paper we study the static and dynamic electron density and spin-density correlation functions of a two-dimensional electron fluid in the quantum Singwi-Tosi-Land-Sjolander theory. The static density and spin-density structure factors S(q) and S ~ (q) and their corresponding pair-correlation functions g(r) and g ~ (r) have been calculated and compared with the available Monte Carlo (MC) simulation data. It is found that the results for S(q) are in good agreement with the MC data except at large values of q for the larger electron density parameter r s . The pair-correlation function g(r) remains positive in the density range examined (1≤r s ≤8) and matches closely with the MC data except at small separations. The spin-dependent pair-correlation functions g ↑↓ (r) and g ↑↑ (r) also satisfy the positive-definite condition. The behavior of the dynamic properties studied is found to be qualitatively similar to the three-dimensional case except for the important difference in the behavior of the dynamic structure factor S(q,ω). It is seen that S(q,ω) exhibits a double-peak structure in the intermediate wave-vector region beyond the plasmon cutoff wave vector. We have also calculated the spin-dependent effective dynamic potentials by combining the spin-symmetric and spin-antisymmetric effective dynamic potentials. The results are compared with the classical Singwi-Tosi-Land-Sjolander theory wherever possible.

Static and dynamic correlation functions of a two-dimensional quantum electron fluid

Collective excitations in liquid rubidium

We have investigated, employing the techniques of molecular-dynamics computer simulation, the onset of the freezing region of a two-dimensional fluid interacting with a Lennard-Jones potential. We have studied the pair-distribution function g(r) and its Fourier transform S(q) for unique, qualitative, and quantitative structural characteristics associated with the onset of freezing and for the validity of a universal freezing criterion. We conclude that such a criterion exists, but its value is sensitive to even slight changes in density and temperature.

Freezing transition of two-dimensional lennard-jones fluids

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