α-SrMnO3电子结构的第一性原理研究

采用平面波赝势方法对钙钛矿型锰酸盐氧化合物α-SrMnO3的电子结构进行了第一性原理研究. 六方钙钛矿型结构α-SrMnO3化合物为磁性绝缘体, 磁基态对应于共面八面体及共顶点八面体间的磁性交换作用均为反铁磁性(AFM), 其禁带宽度为1.6 eV; 费米能级附近的Mn3d态与O2p态存在很强的杂化作用, 属于共价绝缘体, 这种强共价性使得Mn4+的自旋磁矩偏离理想值. 采用Noodleman的对称性破缺方法, 根据α-SrMnO3不同磁有序态的总能量拟合出α-SrMnO3中的自旋交换耦合常数. α-SrMnO3的局部微结构(Mn—O—Mn)决定了整个体系的特殊磁性交换作用. 共面及共顶点的八面体间均存在AFM交换作用, 并且共顶点八面体间的AFM作用比较强.

First-Principles Study on the Electronic Structures of α-SrMnO3

The electronic structures of hexagonal α-SrMnO3 were studied by first-principles calculations within plane wave pseudopotential method. The calculated results indicate that the α-SrMnO3 is antiferromagnetic(AFM) magnetic insulator at 0 K, and the band gap is about 1.6 eV. The most stable magnetic ground state of hexagonal layed SrMnO3 displays the spin configuration of AFM coupling both within the face-sharing Mn2O9 dimer entity and between the corner-sharing octahedron. There are very strong hybridizations between the Mn3d and O2p states around Fermi level. α-SrMnO3 belongs to covalent insulator, and these strong covalent interactions lead to the deviation from the ideal spin magnetic moment of the Mn4+. The spin exchange coupling constants are fit within the Noodleman's broken symmetry methods through the calculated total energy for the various spin ordered states of α-SrMnO3. The local microstructures(Mn—O—Mn) of α-SrMnO3 determine the special magnetic exchange interaction. There are AFM exchange interactions both within the Mn2O9 entities and between the Mn ions in the corner-sharing octahedron of α-SrMnO3, and the latter AFM exchange interaction is stronger than the former one.