Color prediction of transition metal nitrides by ab-initio methods

Transition metal nitrides have been used as decorative coating materials because of their high hardness and lustrous color. While the electronic structure of these materials is relatively well understood, their color and its variation by defects are still considered as a topic in the area of empirical approach. Here we present a procedure for color-prediction from first principles. Both the intraband and the interband transitions are considered to determine the optical properties and the color. The dielectric function and the reflectivity of the compounds are calculated and then used to obtain the RGB color codes. It is found that calculating the screened plasma frequency and the metal d band correctly is critical to reproduce the color observed in experiment. The effects of interstitial defects are also discussed.