LiOsO $_3$和NaOsO $_3$的结构、电子、磁性和动力学性质的比较从头算研究
Comparative ab initio study of the structural, electronic, magnetic, and dynamical properties of LiOsO$_3$ and NaOsO$_3$
摘要：
尽管LiOsO $_3$和NaOsO $_3$具有相似的化学组成，但它们具有显著不同的结构、电子、磁性和光谱性质。在低温下，LiOsO $_3$是一种极性坏金属，具有菱形$R3c$结构，不存在长程磁序，而NaOsO $_3$是一种$G$型反铁磁绝缘体，具有正交$Pnma$结构。通过比较第一性原理DFT+ $U$计算，考虑了自旋轨道耦合，（$i$）确定不同结构的起源（$R3c$对$Pnma$）特性，（$ii$）提供的证据表明，所有考虑的交换相关泛函（LDA，PBE，PBESol，SCAN和HSE 06）和自旋无序多晶型描述不能同时准确描述两个系统的电子和磁性，和（$iii$）阐明了不同的电子（金属与绝缘）性质主要来源于协同的空间效应和磁效应。最后，我们发现，虽然在环境压力下的LiOsO $_3$与$Pnma$对称性和NaOsO $_3$与$R\bar{3}c$对称性是积极不利的，他们不显示软声子，因此是动态稳定的。预测了LiOsO $_3$从$R3c$到$Pnma$的压力诱导结构相变，而NaOsO $_3$在所考虑的压力范围内没有发现对称性变化。
英文摘要：
Despite similar chemical compositions, LiOsO$_3$ and NaOsO$_3$ exhibit remarkably distinct structural, electronic, magnetic, and spectroscopic properties. At low temperature, LiOsO$_3$ is a polar bad metal with a rhombohedral $R3c$ structure without the presence of long-range magnetic order, whereas NaOsO$_3$ is a $G$-type antiferromagnetic insulator with an orthorhombic $Pnma$ structure. By means of comparative first-principles DFT+$U$ calculations with the inclusion of the spin-orbit coupling, we ($i$) identify the origin of the different structural ($R3c$ vs. $Pnma$) properties using a symmetry-adapted soft mode analysis, ($ii$) provide evidence that all considered exchange-correlation functionals (LDA, PBE, PBEsol, SCAN, and HSE06) and the spin disordered polymorphous descriptions are unsatisfactory to accurately describe the electronic and magnetic properties of both systems simultaneously, and ($iii$) clarify that the distinct electronic (metallic vs. insulating) properties originates mainly from a cooperative steric and magnetic effect. Finally, we find that although at ambient pressure LiOsO$_3$ with a $Pnma$ symmetry and NaOsO$_3$ with a $R\bar{3}c$ symmetry are energetically unfavorable, they do not show soft phonons and therefore are dynamically stable. A pressure-induced structural phase transition from $R3c$ to $Pnma$ for LiOsO$_3$ is predicted, whereas for NaOsO$_3$ no symmetry change is discerned in the considered pressure range.
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