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Abstract:

An approximate but soluble single-site theory for the density of states of a two-band spatially disordered system, the single super-chain approximation/effective-medium approximation (SSCA/EMA), is compared with direct simulations on and off-diagonally disordered, two-level tight-binding model. The theory reproduces the simulations remarkably well.

Abstract:

The adequacy and range of applicability of an analytically soluble single site theory for the density of states of a spatially disordered system is assessed by comparison with numerical simulations on an off-diagonally disordered tight-binding model. The validity of a non-single site theory, appropriate in the low-density domain, is also examined by comparison with simulation.

Abstract:

A molecular theory is given for the thermodynamic state dependence of the Raman noncoincidence effect, arising from transition dipolar resonant transfer in dipolar binary liquid mixtures. Predictions of the theory are discussed, and some suggestions for possible experiments are made. © 1989.

Abstract:

The results of simulation studies of the localization and quantum-transport characteristics of a three-dimensional, off-diagonally disordered tight-binding model are reported. The disorder is characteristic of a hard-sphere fluid, with an exponential transfer-matrix element. The properties calculated include the density of states, the band-edge and mobility-edge trajectories, and the time dependence of the averaged probability, P»(t), that an excitation will be found at the site at which it was initially located. Localization of eigenstates is inferred from a criterion based on a cutoff in the inverse participation ratio, and an attempt is made to provide a reasoned estimate for the chosen cutoff via time-dependent studies of P»(t). Pronounced screening effects on the band-edge and mobility-edge trajectories are found and their physical origin is discussed. The consequences of varying the ratio of the hard-sphere diameter to the range of the exponential interaction are investigated. The results obtained for the hard-sphere fluid are contrasted with those for a randomly substituted lattice at the same density. © 1988 The American Physical Society.