The properties of materials and nanostructures are determined by the delicate interplay of electronic and nuclear degrees of freedom. The electrons are to a larhe extent quantal while the motion of the heavier nuclei gives rise to vibrational quanta called phonons, which can sometimes be described using classical dynamics. Bulk systems are typically periodic while nanosystems are finite and therefore much more difficult to describe. Electronic structure is the theory of the charge carriers in materials and nanostructures.