Polymorphism and metastability in NbN: Structural predictions from first principles.

摘要: We use ab initio pseudopotential total-energy calculations with a plane-wave basis set to investigate the structural energetics of various phases polymorphic NbN. Particular attention is given its recently discovered superconducting phase ${\mathit{T}}_{\mathit{c}}$ 16.4 K, reported have NbO structure type. Results show that it in fact energetically unfavorable for NbN form this cubic structure, and predicted theoretical lattice constant significantly smaller than experimental value. Various approaches identification an alternative are discussed. In preliminary investigations, we found two structures more favorable structure.