Electronic Structure and Superconductivity of Compressed Metal Tetrahydrides
Electronic Structure and Superconductivity of Compressed Metal Tetrahydrides
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DOI：
10.1002/chem.202102679
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发表时间：
2021-09-24
影响因子：
4.3
通讯作者：
Zurek, Eva
中科院分区：
文献类型：
--
作者：
Bi, Tiange;Zurek, Eva
已经预测在ThCr 2Si 2结构类型中结晶的四方晶系在压力下对于过多的金属变得稳定，并且最近已经合成了一些。通过详细的第一性原理研究，我们表明，这些I4/mmm对称MH 4化合物中的金属原子可能是二价，三价或四价。金属原子的价态及其半径决定了这些相的成键和电子结构，以及它们在压力下的演化。对于增强超导性的重要因素包括在费米能级处的大量类氢态，以及准分子H2 δ-单元的存在，其键通过来自正电性金属的电子转移以及通过与金属的库巴斯样相互作用而被拉伸和削弱（但未断裂）。MgH_4、ScH_4和ZrH_4超导的微观机制分析表明，声子模式涉及H_2 δ-单元的耦合振动和拉伸，导致更复杂的类氢基序的形成，是电子-声子耦合机制的重要贡献者。在二价氢化物MgH 4中，与双价氢原子的运动相关的模式也是关键贡献者，并且在较低压力下基本上软化。
Tetrahydrides crystallizing in the ThCr2Si2 structure type have been predicted to become stable for a plethora of metals under pressure, and some have recently been synthesized. Through detailed first-principles investigations we show that the metal atoms within these I4/mmm symmetry MH4 compounds may be divalent, trivalent or tetravalent. The valence of the metal atom and its radius govern the bonding and electronic structure of these phases, and their evolution under pressure. The factors important for enhancing superconductivity include a large number of hydrogenic states at the Fermi level, and the presence of quasi-molecular H2 delta- units whose bonds have been stretched and weakened (but not broken) via electron transfer from the electropositive metal, and via a Kubas-like interaction with the metal. Analysis of the microscopic mechanism of superconductivity in MgH4, ScH4 and ZrH4 reveals that phonon modes involving a coupled libration and stretch of the H2 delta- units leading to the formation of more complex hydrogenic motifs are important contributors towards the electron phonon coupling mechanism. In the divalent hydride MgH4, modes associated with motions of the hydridic hydrogen atoms are also key contributors, and soften substantially at lower pressures.