If you are studying Solid State Physics, or in Condensed Matter, this may be of interest to you if you haven't found it already. Practically everyone in this field would have had to deal with the Harrison's theory of tight-binding model in calculating the "simple" band structure of solids. This is also the clearest indication why atoms in solids cannot be thought of as having the same properties as atoms in isolation - the valence shell can be severely changed due to significant overlapping with neighboring atoms. Solid State physics texts such as Kittel's and Ashcroft/Mermin's have ample introduction to this topic, but I also recommend the two Harrison's book now published by Dover (which incidentally, also contain a very good chapter on transport properties via the Boltzmann transport equation). Anyway, this is all leading to a paper just published in Phys. Rev. B that produces a "modification and extension" to the tight-binding theory. As we all know, the standard tight-binding theory only works in a limited range, and could not accurately duplicate the band structure of transition metals, for example. These new modifications/extensions claim to improve at least the ground state band structure, while keeping the same "theme" of the original theory but with modified hopping parameters. In any case, this I think would be a good read for people in this field, and may even be a good undergraduate senior project. L. Shi and D.A. Papaconstantopoulos, Phys. Rev. B v.70, p.205101 (2004) Zz.