This work presents a Tight Binding method designed for the evaluation of the electronic configuration of nanostructures of a large size. The method has been applied to SnO2 nanocrystalline grains. In fact, in spite of its many practical applications, the lattice and composition of this material represent a severe test for computational methods of whichever accuracy, and the number of studies devoted to its characterization is extremely limited. In this study grains with shape and size comparable to the experimental ones are considered. The grains lattice has the rutile structure, as in the bulk, and may also include vacancy defects. The calculations focus on the grain cohesion and describe the dependence of this quantity on the structural grain parameters, i.e. size, shape and defect type. The results are compared to Density Functional calculations also carried out in the course of this study.