The Kitaev model of spin-1/2 on a honeycomb lattice supports degenerate topological ground states and may be useful in topological quantum computation. Na$_{2}$IrO$_{3}$ with honeycomb lattice of Ir ions have been extensively studied as candidates for the realization of the this model, due to the effective $J_{\text{eff}}=1/2$ low-energy excitations produced by spin-orbit and crystal-field effect. As the eventual realization of Kitaev model has remained evasive, it is highly desirable and challenging to tune the candidate materials toward such end. It is well known external pressure often leads to dramatic changes to the geometric and electronic structure of materials. In this work, the high pressure phase diagram of Na$_{2}$IrO$_{3}$ is examined by first-principles calculations. It is found that Na$_{2}$IrO$_{3}$ undergoes a sequence of structural and magnetic phase transitions, from the magnetically ordered phase with space group $C2/m$ to two bond-ordered non-magnetic phases. The low-energy excitations in these high-pressure phases can be well described by the $J_{\text{eff}}=1/2$ states.
First-principles study of the charge ordered phase in $κ$-D$_3$(Cat-EDT-TTF/ST)$_2$: Stability of $π$-electron deuterium coupled ordering in hydrogen-bonded molecular conductors
Coexisting Z-type charge and bond order in metallic NaRu$_2$O$_4$
量子材料中特殊的键是如何形成的，一直是一个长期存在的难题。处理电荷自由度的两个关键概念是二聚（形成金属-金属键）和电荷有序（CO）。自20世纪30年代以来，这两个概念经常被用来解释许多令人兴奋的量子材料，通常是绝缘体。在这里，我们报告的二聚体和CO内共存的金属NaRu $_2$ O $_4$。通过结合高分辨率的X射线衍射研究和理论计算，我们证明了这种独特的现象是通过一种新型的键合发生的，我们称之为Z型有序。低温超结构在Z字形梯的腿部有较强的二聚化作用，腿部的短二聚体通过短Z字形键连接，形成Z形簇;同时，也出现了中心电荷有序。我们的研究结果表明，量子材料的轨道，电荷和晶格自由度之间的复杂相互作用的未知的灵活性。
Electronic structure and chemical bonding in novel tetragonal phase Ca10(Pt4As8)(Fe2As2)5 as a parent material for the new family of high-TC iron-pnictide superconductors
Effect of iron-doping on spin-state transition and ferromagnetism in Pr$_{0.5}$Ca$_{0.5}$CoO$_{3-δ}$ cobalt oxides
对多晶Pr $_{0.5}$ Ca $_{0.5}$ Co $_{1-x}$ Fe $_{x}$ O $_{3-δ}$（$x$ = 0、0.05、0.10和0.15）样品进行电阻率和直流磁化测量。所制备的样品表现出铁磁（FM）转变，转变温度随着铁掺杂量的增加而增加。高氧压退火诱导了\emph{iron-free}样品中Co离子的自旋态转变，并且这种转变随着退火氧压的增加而增强，而高氧压退火抑制了铁磁有序。与\emph{iron-free}样品的情况相反，\emph{iron-doped}样品在高氧压下退火没有引起自旋态转变，并且铁磁转变温度几乎与退火过程无关。\emph{iron-free}样品在高氧压下退火后自旋态转变的增强应归因于晶胞体积的减小。Fe掺杂对自旋态跃迁的抑制与晶胞体积的增大以及Fe-O键比Co-O键强有关。铁掺杂对铁磁性的增强可能源于Fe $^{3+}$和Co $^{4+}$之间通过氧的铁磁交换相互作用（Fe $^{3+}$ -O-Co $^{4+}$）。
Spontaneous ordering as an intrinsic effect at the mesoscopic scale: A vibrational insight in (Zn,Be)Se by Raman scattering and first-principles calculations
Bond orientational ordering in liquids: Towards a unified description of water-like anomalies, liquid-liquid transition, glass transition, and crystallization
