Tetragonal crystalline carbon nitrides: Theoretical predictions

New tetragonal phases of crystalline carbon nitride (CN) and their atomic s tructures have been identified using a self-consistent-charge density-funct ional tight-binding method. A tetragonal rocksalt structure provides theore tical support to recent experimental evidence for a stoichiometric CN phase with tetragonal symmetry. A body-centered tetragonal CN phase with 1:I sto ichiometry is predicted to be highly stable and of interesting atomic struc ture with complicated C-C and N-N dimerizations along the c axis. The cubic -to-tetragonal transitions are carefully examined to understand the underly ing mechanism.