Electrides with Dinitrogen Ligands.

Electrides are a class of materials which contain excess electrons occupying the cavities in the crystal and playing the role of anions. To achieve electron-rich conditions, it usually requires a positive total formal charge in electride materials. However, the assignment of charges relies on a detailed analysis on chemical bonding. Herein, we present a survey on potential electrides which may be overlooked if no bonding analysis is performed. By applying various structure sampling techniques in conjunction with first-principles calculation, we predicted two compounds Ba2N2:e- and Li2Ca3N6:2e-, both of which are featured by the presence of dinitrogen ligands [N2], to be potential electrides. While Li2Ca3N6:2e- with [N2]2- ions has been synthesized in the past, its electride nature was discovered for the first time based on our high-throughput screening. On the other hand, Ba2N2:e- with [N2]3- ions is a new compound entirely from first-principles structure prediction. The different valence states of dinitrogen ligands identified in these two compounds suggest a novel route to tune the concentration and anisotropic properties of anionic interstitial electrons. Our discovery does not only establish a new class of inorganic electrides but also demonstrates the predictive power of modern crystal structure sampling techniques toward rational material design.