CHEMICAL ASSOCIATION AND ELECTRONIC-STRUCTURE - A NEW THEORETICAL APPROACH

Chemical association introduces essential modifications in the microsc opic structure of disordered materials, as new species are formed and the density of reactants deceases. These radical changes in the micros copic structure cannot be adequately captured by the pair distribution function, and hence descriptions of the electronic structure at the l evel of the effective medium approximation break down. We here propose a novel approach closely connected with the single superchain/effecti ve medium approximation, in which the effects of chemical association are explicitly built-in. The new approximation has been tested in a si mple minded model of alkali metal, namely a hard sphere fluid with a o ne-level tight-binding Hamiltonian with transfer matrix elements model ed by Yukawa terms. This fluid is thought to undergo a dimerization pr ocess to yield hard dumbbells via an intermediate stage in which a mix ture is present. The proposed approach reproduces the band structure o btained by direct diagonalization for various stages along the reactio n path, while retaining the simplicity of a linear theory. (C) 1998 Am erican Institute of Physics.