Ab initio search of carbon nitrides, isoelectronic with diamond, likely to lead to new ultra hard materials

Covalently bonded networks of carbon nitride materials are expected to possess outstanding physical properties such as high bulk moduli, wide band gap and high thermal conductivity. As a consequence they are nowadays widely investigated both experimentally and theoretically as potential candidates for new ultra-hard materials likely to replace expensive diamond in its different applications. We here give an overview of recent research works using up-to-date, first principles computational methods based on the local density approximation (LDA) of the density functional theory (DFT), in order to closely examine ground state as well as excited states properties of carbon nitrides. Our purpose is twofold: 1) to achieve a quantitative prediction of the hardness for different phases of the C₃N₄ system with a description of their chemical bonding properties; and 2) to extract modelled spectroscopic quantities such as 1s core ionisation energies to help experimentalists assessing the properties obtained from X-ray absorption spectra of the synthesised carbon nitrides.