Towards a metallic quasi‐d 9 system without copper: AgO at high pressure

AgO is a prototypical mixed‐valence compound, with markedly different coordination environment of dumbbell Ag(1+) and low‐spin square‐planar Ag(3+) which render it a narrow band gap semiconductor. The hybrid HSE06 functional reproduces fairly well the band gap of its P 2 1 / c form at ambient conditions (Δ E exp = 1.0–1.1 eV, Δ E theor = 0.94 eV) and suggest progressive band gap decrease with external pressure with metallization at 50 GPa via band overlap. Dynamic (phonon) instability appears at the onset of metallization leading to a structural phase transition to a more stable but still metallic P 1 ̄form. The density of electronic states at the Fermi level of the P 1 ̄polymorph is small and a pseudo‐gap at the Fermi level is preserved.Illustration of the predicted P 2 1 / c → P 1 ̄transformation.(© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)