band theory of solids - definition - condensed matter

Definition: For atoms brought together to form a crystalline solid, their outermost electrons are influenced by a periodic potential function, so that their possible energies forms bands of allowed values separated by bands of forbidden values (in contrast to the discrete energy states of an isolated atom). These electrons are not localised or associated with any particular atom in the solid. This band structure is of fundamental importance in explaining the properties of metals, semiconductors and insulators.