CrN中原子位移的第一性原理计算研究

Atomic distortion in CrN:A first-principle investigation

采用第一性原理计算方法研究了氮化铬(Chromium Nitride,CrN)的正交(Orthorhombic)相,发现其中的Cr原子和N原子均沿着正交结构的[100]方向移动,均偏离其高对称位置,且在结构中形成锯齿形的原子链,这个现象在过去的计算研究中一直没有被考虑.结果表明,在正交相中,原子位移可以使总能降低0.125 eV,因而更加稳定;考虑原子位移后,计算得到的晶格长度等结构参数与实验符合得更好;计算得到的体弹性模量K0数值明显减小,更加接近实验值.正交相的磁基态是层间不对称的反铁磁结构,原子位移是由正交相中层间不对称的磁应力所驱动,同时原子位移可以补偿层间的磁相互作用力.此外,原子位移不改变CrN的莫特绝缘体特性,但是会轻微减小带隙.

First principle calculations indicate that Cr and N atoms in the orthorhombic phase of CrN(Chromium Nitride)tend to shift from their ideal positions along the[100]direction.This shift can induce zigzag Cr-N-Cr chains in the orthorhombic phase;these atomic distortions have not been taken into account in previous studies.The atomic distortions may decrease the total energy of the orthorhombic phase by 0.125 eV/formula unit and make the structure more stable.Lattice constants,moreover,may also be in better agreement with experiment results when considering these atomic distortions.Further,the bulk modulus K0 decreases significantly when considering the atomic distortions and is closer to the experimental value.The atomic distortions are induced by the asymmetric magnetic forces between asymmetric magnetic layers in the special antiferromagnetic order of the orthorhombic phase,which compensates for the magnetic forces between the layers.The atomic distortions would not change the Mottinsulator property of the orthorhombic phase but may reduce the band gap slightly.