Chin. Phys. Lett.  2016, Vol. 33 Issue (03): 036202    DOI: 10.1088/0256-307X/33/3/036202
 CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES |
Ground-State Structure and Physical Properties of NB$_{2}$ Predicted from First Principles
Jing-He Wu, Chang-Xin Liu**
Department of Physics, Henan Institute of Education, Zhengzhou 450046
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Abstract Using the newly developed particle swarm optimization algorithm on crystal structural prediction, we predict a new class of boron nitride with stoichiometry of NB$_{2}$ at ambient pressure, which belongs to the tetragonal $I\bar{4}m2$ space group. Then, its structure, elastic properties, electronic structure, and chemical bonding are investigated by first-principles calculations with the density functional theory. The phonon calculation and elastic constants confirm that the predicted NB$_{2}$ is dynamically and mechanically stable, respectively. The large bulk modulus, large shear modulus, large Young's modulus, and small Poisson's ratio show that the $I\bar{4}m2$ NB$_{2}$ should be a new superhard material with a calculated theoretical Vickers hardness value of 66 GPa. Further analysis on density of states and electron localization function demonstrate that the strong B–B and B–N covalent bonds are the main reason for its high hardness in $I\bar{4}m2$ NB$_{2}$.
Received: 20 December 2015      Published: 31 March 2016
 PACS: 62.20.D- (Elasticity) 62.20.de (Elastic moduli) 62.20.dq (Other elastic constants) 63.20.dk (First-principles theory) 31.15.ae (Electronic structure and bonding characteristics)
 Cite this article: Jing-He Wu, Chang-Xin Liu 2016 Chin. Phys. Lett. 33 036202 URL: http://cpl.iphy.ac.cn/10.1088/0256-307X/33/3/036202       OR      http://cpl.iphy.ac.cn/Y2016/V33/I03/036202