Liu Shanshan, Xu Yuanhui, Cui Yanli, Wang Jing, Sun Keju, Yu Shengxue, Hao Xianfeng
Department of Chemical Engineering, Key Laboratory of Applied Chemistry, Yanshan University, Qinhuangdao 066004, People's Republic of China.
J Phys Condens Matter. 2017 Aug 9;29(31):315501. doi: 10.1088/1361-648X/aa76be. Epub 2017 Jun 27.
The structural, electronic and magnetic properties of a charge-ordered iron fluoride material CsFeFeF have been explored by density functional theory calculations based on the generalized gradient approximation + U approach, which was implemented in the VASP code. The material exhibits a 3D pyrochlore-related structure which consists of corner-shared FeF and FeF octahedra. Our results confirm that CsFeF is a Mott-Hubbard insulator, and bears a magnetically frustrated ground state in which the localized 3d electrons are antiferromagnetically coupled between the homogeneous Fe ions (Fe-Fe along the b axis, and Fe-Fe along the a axis), while interactions between the heterogeneous Fe ions (Fe-Fe along the c axis) are frustrated, consistent with Goodenough-Kanamori superexchange interactions. Although the disproportionation of the total 3d charge is extremely low, explicit evidence is provided on the charge ordering by an order parameter, which is defined as the difference in minority d orbital (in the local coordinates) occupations between the Fe and Fe cations. In addition, spin ordering and the spin-orbit coupling effect play an insignificant role in the charge ordering and the preferential occupation of the d orbital scenario in CsFeF.
基于广义梯度近似+U方法，利用VASP代码进行密度泛函理论计算，对电荷有序的氟化铁材料CsFeFeF的结构、电子和磁性性质进行了研究。该材料呈现出一种与三维烧绿石相关的结构，由角共享的FeF和FeF八面体组成。我们的结果证实，CsFeF是一种莫特-哈伯德绝缘体，具有磁阻挫基态，其中局域化的3d电子在均匀的Fe离子之间反铁磁耦合（沿b轴的Fe-Fe，以及沿a轴的Fe-Fe），而异质Fe离子之间（沿c轴的Fe-Fe）的相互作用受到阻挫，这与古迪纳夫-金森超交换相互作用一致。尽管总3d电荷的歧化程度极低，但通过一个序参量提供了电荷有序的明确证据，该序参量定义为Fe和Fe阳离子之间少数d轨道（在局部坐标中）占据情况的差异。此外，自旋有序和自旋-轨道耦合效应在CsFeF的电荷有序和d轨道优先占据情况中起的作用不显著。
