Application of induction procedure and Smith decomposition in calculation and topological classification of electronic band structures in the 230 space groups

The electronic properties in a solid depend on the specific form of the wave functions that represent the electronic states in the Brillouin zone. Since the discovery of topological insulators, much attention has been paid to the restrictions that the symmetry imposes on the electronic band structures. In this work we apply two different approaches to characterize all types of bands in a solid by the analysis of the symmetry eingenvalues: the induction procedure and the Smith decomposition method. The symmetry eigenvalues or irreducible representation (irreps) of any electronic band in a given space group can be expressed as the superposition of the eigenvalues of a relatively small number of building units (the basic bands). These basic bands in all the space groups are obtained following a group-subgroup chain starting from P1. Once the whole set of basic bands are known in a space group, all other types of bands (trivial, strong topological, or fragile topological) can be easily derived. In particular, we confirm previous calculations of the fragile root bands in all the space groups. Furthermore, we define an automorphism group of equivalences of the electronic bands which allows to define minimum subsets of, for instance, independent basic or fragile root bands.