My calculus is very rusty, I have this integral that I need to evaluate for different geometries. g are lattice vectors, r the realspace vectors - so I need to evaluate so for each g over the surface of the required geometry.

$\displaystyle \oint{ds\exp{-ig\cdot r}}$

(in case my latex doesn't work the equation is: integral over closed surface of ds.exp(-ig.r))

This possibly isn't a very coherent question - but I just don't have a clue where to start with this. Any help would be very much appreciated.

jbd