Orbital occupation selects structural dimensionality in binary transition-metal oxides
Abstract
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 eg electron of high-spin Cr2+ gives rise to two competing orbital-structure states. The dx2−y2 occupation favors a three-dimensionally connected covalent phase, whereas the dz2 occupation stabilizes a weakly coupled layered phase. Constrained-occupation calculations show that increasing the dz2 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.
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BibTeX
@misc{guo2026orbital,
title = {{Orbital occupation selects structural dimensionality in binary transition-metal oxides}},
author = {Deping Guo and Renhong Wang and Cong Wang and Meng Gao and Wu Zhou and Yanning Zhang and Fei Pang and Zhihai Cheng and Wei Ji},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.28996},
eprint = {2608.28996},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.28996},
}
RIS
TY - UNPB
TI - Orbital occupation selects structural dimensionality in binary transition-metal oxides
AU - Deping Guo
AU - Renhong Wang
AU - Cong Wang
AU - Meng Gao
AU - Wu Zhou
AU - Yanning Zhang
AU - Fei Pang
AU - Zhihai Cheng
AU - Wei Ji
PY - 2026
DA - 2026/08/29
PB - arXiv
DO - 10.48550/arxiv.2608.28996
UR - https://arxiv.org/abs/2608.28996
AB - 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.
ER -