Ab initio study of energetic solids: cupric azide, mercuric azide, and lead azide

We presented a detailed study on the electronic structure and optical properties of cupric azide (Cu(N(3))(2)), mercuric azide (alpha-Hg(N(3))(2)), and lead azide (alpha-Pb(N(3))(2)) by using density functional theory within the generalized gradient approximation. Relaxed crystal structures compare well with experimental data. An analysis of electronic structure, charge transfer, and bond order shows that Cu(N(3))(2) and alpha-Hg(N(3))(2) are covalent-type solids, whereas alpha-Pb(N(3))(2) is an ionic-type solid but has weak covalent character. The valence bands of Cu(N(3))(2) and alpha-Hg(N(3))(2) arise from the contributions of the metal-d and N-p states, whereas that of alpha-Pb(N(3))(2) are strongly dominated by N-p states and not from Pb-d states. The general shapes of the real and imaginary parts of the dielectric function, adsorption coefficient, and photoconductivity spectra for the three azides are similar. Our calculated optical properties are found to be in agreement with available experimental data. The absorption spectra show a number of absorption peaks in the fundamental absorption region. All the photoconductivity spectra display a broad photocurrent response in the fundamental absorption region. The density of states of the three azides reveal the effects of the metal states on the valence electron of the azide group and so are correlated with their impact sensitivity.