Theoretical calculations on the structural, electronic, and optical properties of bulk silver nitrides

The extreme endothermic nature of silver nitride has been hampering its experimental characterization and there is incomplete detailed knowledge of the structural and physical properties of this material. Stimulated by this lack, we present a first-principles DFT and GW investigation of structural, electronic, and optical properties of bulk crystalline silver nitrides. In this study, 20 structures for Ag3N, AgN, and AgN2 were investigated. The equilibrium cohesive and formation energies revealed that the AgN2 series contains the most energetically stable phases. However, all the formation energies confirmed that silver nitrides are thermodynamically unstable. New possible structural phase transitions were discovered from the enthalpy-pressure equation of states diagrams. We predict that the most stable phases of AgN and AgN2 are metallic, while those of Ag3N are semiconductors. In agreement with a previous study, it is found that as the nitrogen to silver ratio decreases, the total DOS at Fermi energy decreases until a gap opens. The calculated lattice parameter of Ag3N(D09)-the most stable modification in the considered Ag3N phases-is close to the experimentally reported one, yet the calculated absorption spectrum does not explain the observed black color of the synthesized Ag3N. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim