This talk was given in February 1998 as a supplementary lecture to
Professor Peter Littlewood's graduate course on correlated electron physics in
the Theory of Condensed Matter Group at the Cavendish Laboratory.
It is a rather crude attempt to explain the status of 'band theory' in
describing the electronic structure of so-called
'strongly-correlated' materials to people more used to model Hamiltonians. Such materials, of which the paradigmatic ones
are probably the 3d monoxides like NiO and the parent compounds of the high-Tc
superconductors such as La2CuO4, have generated intense interest in the last
twenty years. You should note that this was a graduate lecture for people not necessarily familiar with electronic structure theory, so it's meant to be clear rather than rigorous..
This is my first attempt to transcribe a talk for the web, and I'm not sure how successful the format is. Basically, the top of each page contains bullet points and figures and was originally an overhead transparency. The italic text after the horizontal line is a rough approximation to what I said at the time.
Thanks to Nic Harrison, Vic Saunders and Roberto Dovesi, who advised me during my Ph.D. studies on this topic from 1991 to 1994.
If you don't want to plough through all thirty overheads, a brief summary of the main points can be found here.
Comments welcome - mailed me at mdt26 at cam.ac.uk .