Steven, Thanks for the response and the midterm/solution link. That problem and the answer captured the subtlety very nicely. I think I have read most of the "band folding" posts in the archive, but had an overly strict definition of super-cell.
Bruce "Steven G. Johnson" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > > No it doesn't. If the dielectric function is a multilayer film and > hence is univariate, the problem can always be reduced to a 1d one > because the other dimensions are separable. In MPB, you would still > specify a 1d unit-cell with two no-size dimensions, and off-axis > propagation is specified simply by giving a k vector that has a > component along one or both of the no-size directions. > > In fact, you *really* don't want to give a non-zero cell size along > the invariant directions, because doing so will result in artificially > folded bands. (This is a common point of confusion. I actually posed > this as a question on the mid-term exam for my nanophotonics course > last year. See question 2 in: > http://www-math.mit.edu/~stevenj/18.369/spring07/midterm.pdf > and the solution in > http://www-math.mit.edu/~stevenj/18.369/spring07/midterm-sol.pdf) > > Your unit cell should be dictated by the periodicity of the structure, > not by the propagation direction. > > Regards, > Steven G. Johnson _______________________________________________ mpb-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/mpb-discuss
