发表机构
Sichuan Normal University; Renmin University of China; University of Chinese Academy of Sciences; University of Electronic Science and Technology of China（四川师范大学; 中国人民大学; 中国科学院大学; 电子科技大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究以CrO为原型，发现轨道占据可决定二元过渡金属氧化物的结构维度，揭示了轨道填充与键合基序偏好的关系，为低维氧化物材料探索提供微观基础。
AI 中文摘要
过渡金属氧化物中的轨道-晶格耦合通常在给定的键合框架内讨论，其中轨道占据与局部配位、应变或对称性破缺相互交织。本文表明，轨道占据还可选择键合框架本身，从而决定结构维度。通过第一性原理计算，我们确定CrO为原型，其中高自旋Cr²⁺的单个活性3d e_g电子产生两种相互竞争的轨道-结构态：d_{x²-y²}占据有利于三维连接的共价相，而d_{z²}占据则稳定弱耦合的层状相。约束占据计算显示，增加d_{z²}填充会连续收缩面内晶格，同时沿层法线方向扩展结构。两种相表现出截然不同的磁基态和铁弹性响应。此外，层状相对交换关联泛函和在位能（U）变化具有鲁棒性，在单层极限下仍保持动力学稳定性，且剥离能低至46 meV/Ų。将分析扩展至相关3d二元氧化物，揭示了可及轨道填充与二维或三维连接键合基序偏好之间的填充依赖关系，为探索低维氧化物材料提供了微观基础。
英文摘要
Orbital-lattice coupling in transition-metal oxides is usually discussed within a given bonding framework, where orbital occupation is intertwined with local coordination, strain, or symmetry breaking. Here, we show that orbital occupation can also select the bonding framework itself, thereby determining structural dimensionality. Using first-principles calculations, we identify CrO as a prototype in which the single active $3d\,e_g$ electron of high-spin Cr$^{2+}$ gives rise to two competing orbital-structure states. The $d_{x^2-y^2}$ occupation favors a three-dimensionally connected covalent phase, whereas the $d_{z^2}$ occupation stabilizes a weakly coupled layered phase. Constrained-occupation calculations show that increasing the $d_{z^2}$ filling continuously contracts the in-plane lattice while expanding the structure along the layer normal. The two phases exhibit distinct magnetic ground states and ferroelastic responses. Moreover, the layered phase is robust against exchange-correlation functional and on-site ($U$) variations, remains dynamically stable down to the monolayer limit, and has a low exfoliation energy of 46 meV/Angstrom^2. Extending the analysis across related $3d$ binary oxides reveals a filling-dependence relation between accessible orbital filling and the preference for 2D or 3D connected bonding motifs, providing a microscopic basis for exploring low-dimensional oxide materials.
