Structural evolution and electronic properties of anionic carbon-nitrogen clusters

Carbon-doped nitrogen clusters have represented a fascinating area of materials science in recent years. However, achieving precise control of the doping level and distribution of carbon within nitrogen clusters is challenging. Advanced techniques are required to elucidate their exact structures and electronic properties. Here, we perform systematic structure searches of anionic carbon-doped nitrogen clusters by the Crystal structure AnaLYsis by Particle Swarm Optimization method combined with density-functional theory calculations. The ground state structures of CN^- (n = 4-16) clusters for each cluster size are determined. The structural evolution, photoelectron energy spectra, electronic properties, and chemical bonding modes of anionic CN^- (n = 4-16) clusters are discussed. The calculated results indicate that the two-dimensional planar geometry of the anionic CN₆^- cluster with the C₁ symmetry exhibits robust stability. The molecular orbitals and the adaptive natural density partitioning calculations show that the high stability of the anionic CN₆^- cluster is attributed to the localized σ-bonding formed by the 2p orbitals of carbon and nitrogen atoms. The four delocalized π chemical bonds contribute to the stability of the anionic CN₆^- cluster, resulting in a stable ring geometry. The present results enrich the database of geometric structures of carbon-nitrogen clusters and provide valuable insights for the experimental synthesis and characterization of nitrogen-based clusters.