Electronic and Magnetic Properties of Isostructural Polycarbonitrides CeCN₅ and TbCN₅ Under Extreme Pressure: A DFT and DMFT Study

Isostructural polycarbonitrides CeCN₅ and TbCN₅ were recently synthesised in diamond anvil cells at pressures between 90 and 111 GPa [1]. They are built up by previously unobserved anionic single-bonded carbon-nitrogen 3D framework consisting of CN₄ tetrahedra connected via di- or oligo-nitrogen linkers. We characterise the electronic, magnetic, and structural properties of these systems using density functional theory (DFT), and the DFT+U method. We present the electronic, magnetic, and structural properties of these two systems at their synthesis pressure and under decompression. Our calculations predict that while isostructural, the two systems have different valence for the rare-earth elements, a property that is sustained for some pressure range as decompression occurs. Apart from a difference in valence the systems show distinctly different electronic and magnetic properties. These points are further confirmed with dynamical mean field theory (DMFT) in the Hubbard-I approximation. As CeCN₅ is decompressed to near ambient conditions an electronic transition occurs, altering also its magnetic and structural properties. The transition is also confirmed by DMFT.



[1] A. Aslandukov, A. Liang, et al., J. Am. Chem. Soc. 146 (26), 2024