In this contribution, we report the results of theoretical calculation on the pressure induced phase transitions, structural, electronic and optical properties of the lithium based ternary LiBeX (X= As, Sb, Bi) compounds. These calculations are carried out using the full potential linearized augmented plane wave method. Our results show that these compounds undergo first order phase transitions. LiBeAs transforms from the reported semiconducting tetragonal Cu2Sb--type structure (P4/nmm) to the semiconducting polar hexagonal LiGaGe--type structure (P63mc) at 3.95 GPa, then to the metallic Ni2In (P63/mmc) structure at 66.62 GPa. In LiBeSb, only one transition occurs at 63.95 GPa from the semiconducting LiGaGe type-structure to the metallic Ni2In one. LiBeBi exhibits two phase transitions, the first one from the semiconducting LiGaGe phase to the MgSrSi one at 50 GPa, then to the metallic Ni2In at 61 GPa. Our calculated structural parameters with the modified generalized gradient approximation (PBEsol) functional are in very good agreement with other experimental and theoretical values available in the literature. The band structure and density of states of the studied compounds in different phases are calculated using PBEsol functional and Tran-Blaha modified Becke-Johnson exchange (mBJ) potential. Studied materials in their different semiconducting phases have indirect band gaps, which are higher with the mBJ potential than those obtained with PBEsol functional. The structures and peaks in the optical spectra are related to the transitions in the band structure. The mean value of $\varepsilon(0)$ increases in this sequence LiBeAs-LiBeSb-LiBeBi. The variation of the dielectric constants with pressure is consistent with the variation of the direct band gaps and shows a discontinuity at the transition. The absorption coefficients, $\alpha_{xx}$ and $\alpha_{zz}$, are the highest for the LiBeBi in the LiGaGe structure in the visible regime. LiBeSb and LiBeBi are promising candidates for application in the visible regime.

中文翻译：

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LiBeX（X= As、Sb 和 Bi）的压力诱导相变、电子和光学性质


在这篇文章中，我们报告了锂基三元 LiBeX（X= As、Sb、Bi）化合物的压力诱导相变、结构、电子和光学性质的理论计算结果。这些计算是使用全势线性化增强平面波方法进行的。我们的结果表明这些化合物经历一级相变。 LiBeAs在3.95 GPa下从报道的半导体四方Cu2Sb型结构（P4/nmm）转变为半导体极性六方LiGaGe型结构（P63mc），然后在66.62 GPa下转变为金属Ni2In（P63/mmc）结构。在 LiBeSb 中，在 63.95 GPa 下仅发生一次从半导体 LiGaGe 型结构到金属 Ni2In 型结构的转变。 LiBeBi 表现出两种相变，第一种是在 50 GPa 下从半导体 LiGaGe 相转变为 MgSrSi 相，然后在 61 GPa 下转变为金属 Ni2In。我们使用改进的广义梯度近似（PBEsol）泛函计算出的结构参数与文献中提供的其他实验和理论值非常一致。使用 PBEsol 泛函和 Tran-Blaha 修改的 Becke-Johnson 交换 (mBJ) 势计算所研究化合物在不同相中的能带结构和态密度。所研究的不同半导体相的材料具有间接带隙，mBJ 电势的间接带隙高于 PBEsol 功能获得的带隙。光谱中的结构和峰与能带结构中的跃迁有关。 $\varepsilon(0)$ 的平均值在此序列 LiBeAs-LiBeSb-LiBeBi 中增加。 介电常数随压力的变化与直接带隙的变化一致，并且在过渡处表现出不连续性。在可见光区，LiGaGe 结构中的 LiBeBi 的吸收系数 $\alpha_{xx}$ 和 $\alpha_{zz}$ 是最高的。 LiBeSb 和 LiBeBi 是在可见光领域应用的有希望的候选者。