Ab initio calculation of the electronic, mechanical, and thermodynamic properties of yttrium nitride with the rocksalt structure

摘要

The electronic, mechanical, and thermodynamic properties of yttrium nitride with the rocksalt structure have been systematically investigated by using the projector augmented wave method. The calculated results compare very well with available experimental and theoretical results. To properly describe the electronic properties, the generalized gradient approximation GGA(PW91)+U and GGA(PBE)+U theoretical formalisms have been employed. Generally, the PW91 functional provides a slightly more optimal agreement with other theoretical results at lower U energy than PBE does. We calculated the elastic constants of YN based on the GGA and GGA+U methods, and obtained the elastic moduli, brittle/ductile characteristics, Possion's ratio, the hardness, various wave velocities, and Debye temperature of YN. It is shown that Hubbard U correction has a certain impact on the mechanical properties of YN. The heat capacity C_v and the entropy S in the temperature range of 0-2200K are obtained based on the phonon method and the Debye model. It is revealed that the entropies obtained by the two methods are consistent with the experiment results. The dependencies of the heat capacity C_p, Debye temperature, the Grüneisen parameter, and the thermal expansion coefficient on pressure and temperature are also obtained in the ranges of 0-120 GPa and 0-2200K by using the Debye model.