The structural and optical properties of lithium azide were studied using density functional theory within the generalized gradient approximation. The crystal structures compare well with experimental data. The ionic character is manifested by the closeness of internitrogen distances to the calculated N-N bond length for the free azide ion. An analysis of electronic structure, charge transfer and bond order is presented. The density of states reproduces the ordering of valence bands from XPS data. Our calculated absorption spectrum shows a number of absorption peaks, which are believed to be associated with different exciton states, in the fundamental absorption region. (c) 2006 Elsevier B.V. All rights reserved.