Normally energy bands are plotted along lines of high symmetry. Those lines criss-cross the 3D 1st BZ. To calculate and plot such bands are very easy in ATK 2010.02, just follow the instructions in the
tutorial on Si. For ATK 2008.10 it's a bit harder, but some inspiration can be found in the
tutorial on band structure plots for 2008.10.
If you want something different, like the energy eigenvalues for a whole set of (kx,ky,kz), evenly distributed in the whole 1st BZ, then first of all: why? I think it will be very difficult to understand such a plot. But second, sure you can (at least it's quite easy in 2008.10), although you'll have to do a bit of programming!
