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An efficient numerical algorithm is given to find the Blum and Ho/ye mean spherical approximation (MSA) solution for binary mixtures of hard-core fluids with one-Yukawa interactions. The initial estimation of the variables is achieved by partial linearization (based on known, physical asymptotic behaviors) of the system of nonlinear equations which result from the Blum and Ho/ye method. The complete procedure is at least one order of magnitude faster than that recently outlined by Giunta et al. More importantly, it always seems to converge to the physical solution (if it exists). We delimit, for several specific mixtures, the density-temperature region where no real solution is possible. This corresponds, following Waisman’s interpretation, to thermodynamic conditions for which vapor–liquid or liquid–liquid separation occurs. The dependency of the MSA solutions on the Yukawa exponent z is studied in detail. For high values of z, adequate for generalized mean spherical approximation (GMSA) applications, we propose an accurate linear approximation, and we relate it to the solutions given by Giunta et al. For equal-sized, symmetric, equimolar binary mixtures, we show that Baxter’s factorized version of the Ornstein–Zernike equation, including the factor correlation functions, can be decoupled. We also find, for equal-sized mixtures, that one of the approximations recently proposed by Jedrzejek et al. using an effective potential method is in very good agreement with our exact (MSA) results. Finally, a theoretical analysis shows that if the Yukawa amplitudes satisfy K12=(K11K22)1/2, the coefficients Dij of the factor correlation functions outside the core are related as follows: D1i/K1i =D2i/K2i, for i=1,2.

New results of parallel transport effects in a GaAs/AlGaAs superlattice are reported. The observations show a positive magnetoconductivity and a linear variation of the conductivity with temperature. The results are best explained by a recent weak-localization theory which explicitly accounts for the superlattice periodic structure. In contrast, neither the standard three-dimensional anisotropic weaklocalization theory nor the two-dimensional one is found to be adequate. This analysis demonstrates the influence of the superlattice structure on parallel charge conduction.

An efficient algorithm is given to find the Blum and Ho/ye mean spherical approximation (MSA) solution for mixtures of hard-core fluids with multi-Yukawa interactions. The initial estimation of the variables is based on the asymptotic high-temperature behavior of the fluid. From this initial estimate only a few Newton–Raphson iterations are required to reach the final solution. The algorithm consistently yields the unique thermodynamically stable solution, whenever it exists, i.e., whenever the fluid appears as a single, homogeneous phase. For conditions in which no single phase can appear, the algorithm will declare the absence of solutions or, less often, produce thermodynamically unstable solutions. A simple criterion reveals the instability of those solutions. Furthermore, this Yukawa-MSA algorithm can be used in a most simple way to estimate the onset of thermodynamic instability and to predict the nature of the resulting phase separation (whether vapor–liquid or liquid–liquid). Specific results are presented for two binary multi-Yukawa mixtures. For both mixtures, the Yukawa interaction parameters were adjusted to fit, beyond the hard-core diameters σ, Lennard-Jones potentials. Therefore the potentials studied, although strictly negative, included a significant repulsion interval. The characteristics of the first mixture were chosen to produce a nearly ideal solution, while those of the second mixture favored strong deviations from ideality. The MSA algorithm was able to reflect correctly their molecular characteristics into the appropriate macroscopic behavior, reproducing not only vapor–liquid equilibrium but also liquid–liquid separations. Finally, the high-density limit of the fluid phase was determined by requiring the radial distribution function to be non-negative. A case is made for interpreting that limit as the fluid–glass transition.

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