COHERENT-POTENTIAL AND AVERAGE T-MATRIX APPROXIMATIONS FOR DISORDERED MUFFIN-TIN ALLOYS .1. FORMALISM

The average density of states (E) and the component charge density associated with an A (B) atom in the alloy, A (B)(E), are discussed for the disordered alloy AxB1-x within the framework of the muffintin Hamiltonian. A new version of the average t-matrix (ATA) is developed. The structure in the spectral density function, (k,E), in the coherent-potential approximation (or the new ATA) is seen to result from not only the Bloch-type states in the medium of coherent-potential effective atoms tCP (or the average t-atoms t) but also from non-Bloch-type impurity levels arising when a single A or B atom is embedded in an otherwise perfect effective medium. The proposed ATA equations would allow a simple yet reliable treatment of many aspects of the electronic spectrum of disordered transition and noble-metal alloys. © 1979 The American Physical Society.