With the theory of density functional calculations we can study the connection between the crystal structure, electronic structure and the properties connected with these. With the comparison of complete energies of different structures we can establish the relative stability of individual structures. With the minimizing of inter-atomic powers we can optimize the position of atoms (ions) in the crystal.

With this method we can accurately calculate also the phonic structure in the super cell which contains 60-100 atoms. As an example of use of TGF I will introduce the study of Y2Nb2O7, which can crystallize in the pyrochlore structure and at the same time works as an isolator.