Optical theorem and multiple-scattering theory: Electronic states in disordered transion-metals
Originally published in Physical Review Letters v.39 (1977): 421-424. DOI: 10.1103/PhysRevLett.39.421
In disordered systems, apparently reasonable decoupling procedures can lead to negative densities of electronic states near resonant d bands. By applying the optical theorem to the multiple-scattering series we can determine a prior whether a given decoupling will necessarily yield positive results. Since none of the extensions of the coherent-potential approximation to amorphous systems is found to meet this requirement, we propose a new scheme which is both self-consistent and guaranteed to give a positive spectrum.
L. Schwartz and A. Bansil. "Optical theorem and multiple-scattering theory: Electronic states in disordered transion-metals" Physics Faculty Publications (1977).
Available at: http://works.bepress.com/abansil/58