Structure, stability, and superconductivity of N-doped lutetium hydrides at kbar pressures

The structure of the material responsible for the room temperature and near ambient pressure superconductivity reported in an N-doped lutetium hydride [Nature (London) 615, 244 (2023)10.1038/s41586-023-05742-0] has not been conclusively determined. Herein, density functional theory calculations are performed in an attempt to uncover what it might be. Guided by a range of strategies including crystal structure prediction and modifications of existing structure types, we present an array of Lu-N-H phases that are dynamically stable at experimentally relevant pressures. Although none of the structures found are thermodynamically stable, and none are expected to remain superconducting above ∼17 K at 10 kbar, a number of metallic compounds with fcc Lu lattices - as suggested by the experimental x-ray diffraction measurements of the majority phase - are identified. The system whose calculated equation of states matches best with that measured for the majority phase is fluorite-type LuH2, whose 10 kbar superconducting critical temperature was estimated to be 0.1 K using the Allen-Dynes modified McMillan equation.