Prediction of the two-dimensional cobalt carbonitride compounds CoN4C10 , Co2N8

Single-atom-thick two-dimensional material containing $3d$ transition metal was rarely reported in the past. Based on the first principles method, we predict that the cobalt carbonitrides ${\mathrm{CoN}}_{4}{\mathrm{C}}_{10}$, ${\mathrm{Co}}_{2}{\mathrm{N}}_{8}{\mathrm{C}}_{6}$, and ${\mathrm{Co}}_{2}{\mathrm{N}}_{6}{\mathrm{C}}_{6}$ are a new class of two-dimensional (2D) materials, which are made up of two components: the ${\mathrm{CoN}}_{4}$ unit and the graphene fragment unit, arranged in a planar pattern. The stability of the ${\mathrm{CoN}}_{4}{\mathrm{C}}_{10}$, ${\mathrm{Co}}_{2}{\mathrm{N}}_{8}{\mathrm{C}}_{6}$, and ${\mathrm{Co}}_{2}{\mathrm{N}}_{6}{\mathrm{C}}_{6}$ monolayers is demonstrated by the formation energy and phonon spectra calculations, as well as the molecular dynamics simulations. The spin-polarized calculations reveal that all three compounds are magnetic metals, and the electronic states near Fermi energy are dominated by Co $3d$ electronic states. Moreover, there exist a few sharp peaks of density of state in the vicinity of Fermi energy, deriving from the ${d}_{{z}^{2}}$ orbitals of Co atom. Thus, the graphenelike transition-metal carbonitrides are not only a new class of 2D materials with single-atom-thickness but also have rich electronic properties due to the incorporation of transition metal.