Importance of cluster distortions in the tetrahedral cluster compounds GaM{sub 4}X{sub 8} (M=Mo,V,Nb,Ta; X=S,Se): Ab initio investigations
Importance of cluster distortions in the tetrahedral cluster compounds GaM{sub 4}X{sub 8} (M=Mo,V,Nb,Ta; X=S,Se): Ab initio investigations
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四面体团簇化合物 GaM{sub 4}X{sub 8} (M=Mo,V,Nb,Ta; X=S,Se) 中团簇扭曲的重要性：从头算研究
DOI：
10.1103/physrevb.76.214106
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发表时间：
2007
影响因子：
3.7
通讯作者：
P. Mohn
中科院分区：
文献类型：
--
作者：
M. Sieberer;S. Turnovszky;J. Redinger;P. Mohn
在本文中，我们研究了所谓的钼簇化合物的选定代表的结构特性。属于该族的是GaM{sub 4}X{sub 8}化合物，其中M=Mo作为VIB族元素并且V、Nb或Ta作为VB族元素。 X表示S或Se。已知这些化合物在电阻率方面表现出半导体行为，这是由电子在分离良好的金属簇之间跳跃引起的。四面体金属（M{sub 4}）簇的大分离被认为是强相关性的根源。我们表明，最近的计算忽略了一种重要的结构畸变类型，即仅在固定角度 {alpha}=60 度的 M{sub 4} 单元内发生的结构畸变。三角形（类面心立方）细胞。与立方晶胞相比，这些内部扭曲获得了大量的能量，而且据我们所知，粉末 X 射线衍射实验几乎无法检测到它们。然而，它们通过在费米能级上打开一个间隙来强烈影响能带结构。然而，这让人怀疑该家族的所有化合物是否真的都是莫特绝缘体，如其他地方所述。特别是，铁磁 GaMo{sub 4}S{sub 8} 和 GaV{sub 4}S{sub 8} 在密度泛函理论中得到了很好的描述。只有 Nb 和更多 » Ta 基代表需要付出巨大的努力，因为反铁磁 M-M 相互作用受挫导致缺乏磁性长程有序。« less
In this paper, we study the structural properties of selected representatives of the so-called molybdenum cluster compounds. Belonging to this family are the GaM{sub 4}X{sub 8} compounds with M=Mo as a group VIB element and V, Nb, or Ta as a group VB element. X denotes either S or Se. These compounds are known to exhibit semiconducting behavior in the electrical resistivity, caused by hopping of electrons between well-separated metal clusters. The large separation of the tetrahedral metal (M{sub 4}) clusters is believed to be the origin of strong correlations. We show that recent calculations neglected an important type of structural distortion, namely, those happening only within the M{sub 4} unit at a fixed angle {alpha}=60 deg. of the trigonal (fcc-like) cell. These internal distortions gain a significant amount of energy compared to the cubic cell and they are--to our knowledge--almost undetectable with powder x-ray diffraction experiments. However, they strongly influence the band-structure by opening up a gap at the Fermi-energy. This, however, puts into question whether all compounds of this family are really Mott insulators as stated elsewhere. In particular, ferromagnetic GaMo{sub 4}S{sub 8} and GaV{sub 4}S{sub 8} are well described within density functional theory. Only the Nb- andmore » Ta-based representatives require a large effort due to the lack of magnetic long-range order caused by frustrated antiferromagnetic M-M interactions.« less