Solving for the dielectric constant that yields a certain gap width

MPB Users & Steven,

    I'm trying to solve a reverse problem of sort. I want set the bandgap of 
my 3D dielectric structure to a certain width, say 1%, and then solve for 
the high index material dielectric value that will yield it, within a 
certain tolerance ofcourse.  For example, an inverted opal would be one of 
my structures.
    My first guess on how to approach this is to give the the program a min 
and max dielectric value in its search, and I start with the median of the 
two. In a loop, I calculate the band structure and if the gap is greater 
that 1% I need to change the dielectric value to between the min and the 
median, in other words the median becomes the new max. If the gaps is less 
that 1%, then I need to work with a dielectric value between the median and 
the max.  It's sorta like a binary search. I would have to put in some 
conditions so that the program doesn't search forever for a complete gap if 
there isn't ever one.
    Does this sound right? Anyone have any thoughts on this, I would 
appreciate any suggestions.

Thanks,

Ian