 leads to delocalized orbitals across two atoms, yielding a covalent bond. Due to the Pauli exclusion principle, every state can contain only one electron.This can be continued with more atoms. Note: This picture shows a metal, not an actual semiconductor.Continuing to add creates a crystal, which may then be cut into a tape and fused together at the ends to allow circular currents.For this regular solid the band structure can be calculated or measured.Integrating over the k axis gives the bands of a semiconductor showing a full valence band and an empty conduction band. Generally stopping at the vacuum level is undesirable, because some people want to calculate: photoemission, inverse photoemissionAfter the band structure is determined states can be combined to generate wave packets. As this is analogous to wave packages in free space, the results are similar.An alternative description, which does not really appreciate the strong Coulomb inter