Ab initio determination of the bulk modulus of the chromium nitride CrN

Abstract

Through ab initio calculations carried out at the hybrid HF/DFT level, we calculate the static energies and the vibrational frequencies of CrN at different cell volumes, in both cubic and orthorhombic geometries. The paramagnetic cubic phase is studied in different magnetic arrangements, whereas the orthorhombic one is studied in the antiferromagnetic configuration. The resulting static energies are fitted by appropriate equations of state to get the static cell volume (V₀), static bulk modulus (K₀) and its pressure derivative (K′). We obtain a static K₀ for the cubic phase ranging from 282 GPa to 302.1 GPa, with a value of K′ that varies from 2.87 to 3.63 and a conventional V₀ oscillating from 73.074 ų to 73.277 ų. At ambient conditions the bulk modulus is reduced by about 6 GPa and the cell volume is increased by about 0.45 ų. For the orthorhombic phase we obtain a value of K₀ ranging from 452.5 GPa to 476 GPa, whose K′ varies from 3.09 to 3.38 and its conventional V₀ oscillates from 73.074 ų to 73.277 ų. At 300 K, K₀ is reduced by about 6 GPa and the V₀ is increased by about 0.45 ų. The computational results here obtained for the orthorhombic phase, although consistent within the methodology used, differ from the very few experimental results on the same phase, and such a difference cannot be explained at the moment. They have to be confirmed by experimental measures in the future.