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Crystal and electronic structure of GaTa_4Se_8 from first-principles calculations

机译：来自第一原理计算的Gata_4se_8的晶体和电子结构

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摘要

GaTa_4Se_8 helongs to the lacunar spinel family and there have heen intensive studies on its novel properties, such as its possible Mott-insulator state and superconductivity under pressure. However, its crystal structure and phase transition are still not well known. In this work, we investigated three different crystal structures, proposed in experiments, using first-principles calculations. For the cubic phase with space group F43m, its phonon spectra have three soft modes in the whole Brillouin zone, indicating the strong dynamical instability. The second one is the trigonal phase with space group R3m, which has been proposed based on Raman spectra under high pressure. This phase can be deduced from the soft phonon modes at Γ of the cubic phase and it is dynamically stable according to its phonon spectra. The third one is the tetragonal phase with space group P42_1m. which is also stable according to its phonon spectra and may be the low-temperature phase from x-ray diffraction. Within local density approximation calculations, the cubic and trigonal phases are metals, while the tetragonal phase is a band insulator consistent with the insulating feature in experiments. Our results suggest the possibility of the non-Mott state of GaTa_4Se_8 at low temperature and ambient pressure as a result of lattice distortion. On the other hand, the electronic structure of the trigonal phase can be viewed as a single-band Hubbard model. The Mott-insulator state has been obtained within dynamical mean-field theory calculation when the interaction parameter U is larger than 0.40 eV vs a bandwidth of 0.25 eV. We hope these findings would be helpful in solving the long-standing problem of the ambiguity in the structural phase of GaTa_4Se_8.
机译：Gata_4se_8 Helongs到Lavunar Spinel家族，并有利于其新颖性质的HEEN密集研究，例如在压力下可能的味道绝缘体状态和超导性。然而，其晶体结构和相转变仍然不熟知。在这项工作中，我们研究了三种不同的晶体结构，在实验中提出，使用了第一原理计算。对于具有空间组F43M的立方相位，其声谱谱在整个布里渊区中具有三种软模式，表明强大的动态不稳定。第二个是具有空间组R3M的Trigonal阶段，这已经基于高压下的拉曼光谱提出。可以从立方相的γ处的软声头模式推导出该阶段，并且根据其声光谱，它是动态稳定的。第三个是间距相位，空间组P42_1M。这也根据其声光谱也稳定，并且可以是来自X射线衍射的低温相。在局部密度近似计算中，立方和三角形相是金属，而四边形相是与实验中的绝缘特征一致的带绝缘体。我们的结果表明，由于格叶的结果，GATA_4SE_8在低温和环境压力下的非味道状态的可能性。另一方面，可以将Trigonal阶段的电子结构视为单频带隆堡模型。当交互参数U大于0.40EV时，在动态平均场理论计算中已经获得了Mott-Insulatir状态，在0.20eV的带宽。我们希望这些发现能有助于解决Gata_4Se_8结构阶段的歧义的长期问题。

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  • 来源
    《Physical review.B.Condensed matter and materials physics》 |2020年第21期|214114.1-214114.7|共7页
  • 作者

    Shuai Zhang; Tiantian Zhang; Hongshan Deng; Yang Ding; Yue Chen; Hongming Weng;

  • 作者单位

    Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China University of Chinese Academy of Sciences Beijing 100049 China;

    Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China Department of Physics Tokyo Institute of Technology Ookavama Meguro-ku Tokyo 152-8551 Japan Tokodai Institute for Element Strategy Tokyo Institute of Technology Nagatsuta Midori-ku Yokohama Kanagawa 226-8503 Japan;

    Center for High Pressure Science and Technology Advanced Research Beijing 100094 China;

    Center for High Pressure Science and Technology Advanced Research Beijing 100094 China;

    Department of Mechanical Engineering The University of Hong Kong Pokfulam Road Hong Kong SAR China;

    Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China University of Chinese Academy of Sciences Beijing 100049 China Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China;

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