Petit L, Svane A, Lüders M, Szotek Z, Vaitheeswaran G, Kanchana V, Temmerman W M
Daresbury Laboratory, Warrington WA4 4AD, UK.
J Phys Condens Matter. 2014 Jul 9;26(27):274213. doi: 10.1088/0953-8984/26/27/274213. Epub 2014 Jun 17.
Using first-principles calculations we have studied the valence and structural transitions of the rare earth monotellurides RTe (R = Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) under pressure. The self-interaction corrected local spin-density approximation is used to establish the ground state valence configuration as a function of volume for the RTe in both the NaCl (B1) and CsCl (B2) structures. We find that in ambient conditions all the RTe are stabilized in the B1 structure. A trivalent (R(3+)) rare earth ground state is predicted for the majority of the RTe, with the exception of SmTe, EuTe, DyTe, TmTe and YbTe, where the fully localized divalent (R(2+)) rare earth configuration is found to be energetically most favourable. Under pressure, the trivalent RTe undergo structural transitions to the B2 structure without associated valence transition. The divalent RTe on the other hand are characterized by a competition between the structural and electronic degrees of freedom, and it is the degree of f-electron delocalization that determines the sequence of phase transitions. In EuTe and YbTe, where respectively the half-filled and filled shells result in a very stable divalent configuration, we find that it is the structural B1 → B2 transition that occurs first, followed by the R(2+) → R(3+) valence transition at even higher pressures. In SmTe, DyTe and TmTe, the electronic transition occurs prior to the structural transition. With the exception of YbTe, the calculated transition pressures are found to be in good agreement with experiment.
我们利用第一性原理计算研究了稀土单碲化物RTe（R = Ce、Pr、Nd、Pm、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm和Yb）在压力下的价态和结构转变。采用自相互作用修正的局域自旋密度近似来确定NaCl（B1）和CsCl（B2）结构中RTe的基态价态构型随体积的变化。我们发现，在环境条件下，所有的RTe都稳定在B1结构中。除SmTe、EuTe、DyTe、TmTe和YbTe外，大多数RTe预测为三价（R(3+)）稀土基态，其中发现完全局域化的二价（R(2+)）稀土构型在能量上最有利。在压力下，三价RTe发生结构转变为B2结构，而没有相关的价态转变。另一方面，二价RTe的特征是结构自由度和电子自由度之间的竞争，正是f电子离域程度决定了相变的顺序。在EuTe和YbTe中，分别是半满壳层和满壳层导致非常稳定的二价构型，我们发现首先发生的是结构从B1到B2的转变，随后在更高压力下发生R(2+)到R(3+)的价态转变。在SmTe、DyTe和TmTe中，电子转变先于结构转变发生。除YbTe外，计算得到的转变压力与实验结果吻合良好。
