  Band alignment effects of anatase and rutile nanocrystals in TiO$_2$ powders
lead to an electron hole separation, increasing the photo catalytic efficiency
of these powders. While size effects and types of possible alignments have been
extensively studied, the effect of interface geometries of bonded nanocrystal
structures on the alignment is poorly understood. In order to allow conclusive
studies of a vast variety of bonded systems in different orientations, we have
developed a new density functional tight binding parameter set to properly
describe quantum confinement in nanocrystals. Applying this set we found a
quantitative influence of the interface structure on the band alignment.
