AI 中文总结
本研究通过多种计算方法探究四方晶系GeS₂和GeSe₂的各向异性热电性质，明确其混合成键特征，发现二者为强各向异性热电材料，面外响应因晶格热输运受抑具中等zT值。
AI 中文摘要
本研究采用密度泛函理论（DFT）、密度泛函微扰理论（DFPT）、Wannier插值及考虑散射的玻尔兹曼输运方法，对四方晶系GeS$_2$和GeSe$_2$的电子结构、晶格动力学、成键、弹性响应及各向异性热电输运性质展开研究。计算得到的弛豫结构在简谐描述范围内具有力学和动力学稳定性。HSE03/Wannier方法计算得到的带隙，GeS$_2$为2.48 eV，GeSe$_2$为1.23 eV；用Se取代S会使最高声子频率从约13.6 THz降至10.3 THz。声子玻尔兹曼输运计算显示出显著的晶格输运各向异性。在弛豫时间近似（RTA）下，300 K时GeS$_2$的面内和面外晶格热导率分别为26.86 W m$^{-1}$ K$^{-1}$和1.19 W m$^{-1}$ K$^{-1}$，GeSe$_2$则为18.74 W m$^{-1}$ K$^{-1}$和1.52 W m$^{-1}$ K$^{-1}$；800 K时，这些值分别降至GeS$_2$的10.22 W m$^{-1}$ K$^{-1}$、0.46 W m$^{-1}$ K$^{-1}$，以及GeSe$_2$的7.25 W m$^{-1}$ K$^{-1}$、0.58 W m$^{-1}$ K$^{-1}$。频率分辨分析表明，低频声子携带大部分热量，而较小的面外值反映了面外声子输运受限。将ShengBTE RTA晶格张量与AMSET电子系数结合，得到800 K、载流子浓度为10$^{19}$ cm$^{-3}$时，n型面外GeS$_2$的热电优值zT=0.257；对应条件下，GeSe$_2$采用PBE-AMSET方法计算，800 K、载流子浓度为3×10$^{20}$ cm$^{-3}$时，p型面外输运的zT=0.066。LOBSTER分析确定Ge-X键为混合共价-离子键，Ge-S键的稳定化积分晶体轨道哈密顿布居（ICOHP）绝对值大于Ge-Se键，分别为-5.27 eV/键和-4.74 eV/键。这些结果表明，四方晶系GeX$_2$化合物是具有中等计算zT值的强各向异性热电材料，其面外响应得益于受抑制的晶格热输运。
英文摘要
The electronic structure, lattice dynamics, bonding, elastic response, and anisotropic thermoelectric transport properties of tetragonal GeS$_2$ and GeSe$_2$ were investigated using density functional theory, density functional perturbation theory, Wannier interpolation, and scattering-aware Boltzmann transport. The relaxed structures are mechanically and dynamically stable within the calculated harmonic description. The HSE03/Wannier band gaps are 2.48 eV for GeS$_2$ and 1.23 eV for GeSe$_2$, while substitution of S by Se lowers the upper phonon frequency from approximately 13.6 to 10.3 THz. The phonon Boltzmann transport calculations reveal pronounced lattice-transport anisotropy. Within the relaxation-time approximation, the 300 K in-plane and cross-plane lattice thermal conductivities are 26.86 and 1.19 W m$^{-1}$ K$^{-1}$ for GeS$_2$, and 18.74 and 1.52 W m$^{-1}$ K$^{-1}$ for GeSe$_2$, respectively. At 800 K, these values decrease to 10.22 and 0.46 W m$^{-1}$ K$^{-1}$ for GeS$_2$, and 7.25 and 0.58 W m$^{-1}$ K$^{-1}$ for GeSe$_2$. Frequency-resolved analysis shows that low-frequency phonons carry most of the heat, whereas the small cross-plane values reflect restricted out-of-plane phonon transport. Combining the ShengBTE RTA lattice tensors with AMSET electronic coefficients gives $zT=0.257$ for n-type cross-plane GeS$_2$ at 800 K and $10^{19}$ cm$^{-3}$. The corresponding PBE-AMSET estimate for GeSe$_2$ is $zT=0.066$ for p-type cross-plane transport at 800 K and $3\times10^{20}$ cm$^{-3}$. LOBSTER analysis identifies mixed covalent--ionic Ge--X bonding, with Ge--S bonds having a larger stabilizing ICOHP magnitude than Ge--Se bonds ($-5.27$ versus $-4.74$ eV per bond). These results identify tetragonal GeX$_2$ compounds as strongly anisotropic thermoelectrics with moderate calculated $zT$ values whose cross-plane response benefits from suppressed lattice heat transport.
Comments31 pages, 25 figures, and 6 tables. Includes supplementary information
