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I don't know if there exists any philosophical discussion of the role for these links in Wikipedia. In my mind, their purpose is to allow the reader to explore not only articles of greater depth on the topic, or items worthy of more elaborate discussion, but articles that are tangentially related to the subject that could widen the reader's appreciation of the general area, akin to browsing a book shelf. So Bloch waves are arguably more closely related to k·p-theory than Wannier functions, but to me both seem appropriate entries. That is particularly so if one is interested in band-structure methods in general, and in a variety of materials (e.g. ferroelectrics). Many of the links in the template are of this nature: they refer to various methods of electronic structure calculation, and not just k·p-theory. Of course, there is no point in duplicating these links, but some related links are included in the See Also section. Brews ohare (talk) 20:57, 15 November 2008 (UTC)
My theory is that this is an encyclopedia article on k·p theory, and everything in this article should be ultimately aimed at the reader better understanding k·p theory. I think a reader would be confused to see an unrelated article like Kohn-Sham equations in the "see also" section. Maybe they would click the link expecting to see some reference to k·p theory in that article, or vice-versa, but they would be disappointed and confused. Sure they both have something to do with band structure, just as this article and string theory both have something to do with perturbation theory. But they're unrelated in the sense that neither subject helps one understand the other. I think navigation templates/boxes are a nice way to get people to browse through articles that aren't directly related to each other, but which all fall under some category of interest. "See also" with no explanation leaves the user guessing what the relationship might be.
See Wikipedia:Guide to layout#"See also" section: "A reasonable number of relevant links that would be in the body of a hypothetical "perfect article" are suitable to add to the "See also" appendix of a less developed one." For example, a really great article on k·p theory would explain how it relates to band gap -- the lower the bandgap, the larger the perturbative corrections and the more nonparabolic the bands, or whatever. This isn't that great an article, so instead of that explanation it only says "see also band gap". That's fine. But no article on k·p theory, no matter how complete, would ever mention the Kohn-Sham equations. So under that guideline, that shouldn't be a see-also.
Plus, if there's too many see-also's, with the really-important ones lumped in with the less-important ones, they'll just all get ignored.
That's my take, but obviously I'm not more of an expert on this than you. I'm eager to hear your response. :-) --Steve (talk) 02:39, 16 November 2008 (UTC)
Hi Steve: Thanks for the reply. Perhaps an approach that would satisfy us both would be patterned after Special_relativity#See_also? In other words, a partition of See Also under categories. Having tried this here, I'd say it looks like a good discipline to apply to every article. Brews ohare (talk) 16:08, 16 November 2008 (UTC)