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Abstract:

We consider the electronic structure of "simple" liquid charge-transfer alloys Cy[CA]1-y, in which the effects of disorder, electron interactions, and their interplay are argued to underly observed experimental behaviour. The primary source of disorder arises from the random Coulomb fields due to both ionic species, and Monte Carlo simulations of the primitive model are undertaken to ascertain the probability densities of local Madelung fields. The electronic structure of the system in the C-rich domain (y > 0) is then considered via numerical study, at a mean-field level, of a spatially and Coulombically disordered Anderson-Hubbard model for the C species conduction band. The results are in accord both with the experimental behaviour of liquid Csy[CsAu]1-y and with recent related theoretical work. © 1994 American Chemical Society.

Abstract:

The presence of disorder, reflecting a range of local environments may lead to local moment formation on an inhomogeneous scale; the essential element of the theory is a self-consistent description of local charges and magnetic moments on sites of different site energies, in , arising from the occurrence of site disorder. The authors consider self-consistently determined local and total pseudoparticle spectra, in -dependent site occupation probabilities, and a measure of the Fermi-level charge distribution over the sites. Particular attention is given to the evolution of the interplay between disorder and interactions as the band filling fraction, y, is increased from y approximately=0 through to the half-filled limit, y=1.

Abstract:

A theory of the dipolar Frenkel excitonic insulator (EI) phase developed in an earlier paper is extended to spatially disordered systems. Using the Hartree approximation studied previously, the authors derive, for a given atomic centre-of-mass configuration, a self-consistency equation for the atomic dipole moments, a non-zero solution to which indicates an EI phase. They obtain as a special case the microscopic Yvon-Kirkwood equations of classical dielectric theory. For the experimentally relevant case of an impurity at infinite dilution in a solvent or disordered matrix, they derive an explicit expression for the impurity dipole moment. To take into account the ensemble of atomic configurations a mean field approximation is developed, numerical results for which, within the class of linear approximations of classical liquid state theory, will be given in a subsequent paper. The authors also examine the dynamic response of the impurity system to an oscillating electric field. They locate the lowest excited state of the system in both the normal insulating and dipolar EI phases, and show that it is degenerate with the ground state at the EI transition, thus making contact with exciton theories of the EI phase.