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arXiv · 2604.19629

Electronic structure and oxidation states in high-pressure synthesized isostructural CeCN$_5$ and TbCN$_5$

Amanda Ehn·Florian Trybel·Talha Bin Masood·Leonid V. Pourovskii·Igor A. Abrikosov
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Abstract

Understanding the behavior of 4$f$ electrons in materials containing rare earth elements is one of the fundamental questions within condensed matter physics. In this work the electronic properties of isostructural CeCN$_5$ and TbCN$_5$, both recently synthesized at extreme pressure, are investigated using Density Functional Theory (DFT) calculations. We include the on-site Coulomb repulsion between localized 4$f$ states within the static DFT+U framework; the DFT+U results are cross-checked with DFT+dynamical mean-field theory (DMFT) calculations within the quasi-atomic (Hubbard-I) approximation. Despite CeCN$_5$ and TbCN$_5$ being isostructural compounds Ce and Tb show different oxidation states, 4+ and 3+ respectively. This leads to distinctly different electronic properties: the former compound is an insulator, while the latter is a metal. An extra electron which is donated by Ce to the polymeric C-N network is distributed across the network. This leads to a modification of the bond length in CeCN$_5$ compared to TbCN$_5$. Still, the polymeric C-N networks can accommodate the different oxidation states in isostructural lanthanide-carbon-nitrogen (LnCN) compounds. Our results underline that LnCN compounds under high pressure offer a unique platform for probing the interplay between 4$f$-electron behavior and structural complexity.

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Amanda Ehn, Florian Trybel, Talha Bin Masood, Leonid V. Pourovskii, Igor A. Abrikosov. 2026-04-21. Electronic structure and oxidation states in high-pressure synthesized isostructural CeCN$_5$ and TbCN$_5$. https://arxiv.org/abs/2604.19629

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