Ab initio study of the electronic and vibrational structures of tetragonal cadmium diarsenide

Ab initio calculations of the electronic spectrum, deformation electron density, and phonon frequencies at the center of the Brillouin zone of the CdAs$_2$ tetragonal compound are carried out in the context of the density-functional method. It is established that the crystal is an indirect-gap semiconductor with a band gap of $\sim$1 eV, which is in good agreement with well-known optical and electrical experimental data. The features of chemical bonding in the crystal are studied. The features are defined by the fact that As atoms form spiral chins of covalent As–As bonds, whereas Cd–As bonds are ionic-covalent. The ab initio calculated phonon frequencies are compared with the frequencies calculated in the Keating model and with experimental data; the partial contributions of Cd and As atoms are analyzed.