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

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 (V-0), static bulk modulus (K-0) and its pressure derivative (K'). We obtain a static K-0 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 V-0 oscillating from 73.074 angstrom(3) to 73.277 angstrom(3). At ambient conditions the bulk modulus is reduced by about 6 GPa and the cell volume is increased by about 0.45 angstrom(3). 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 V-0 oscillates from 73.074 angstrom(3) to 73.277 angstrom(3). At 300 K, K-0 is reduced by about 6 GPa and the V-0 is increased by about 0.45 angstrom(3). 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.