Crystal-field effects competing with spin-orbit interactions in ${\mathrm{NaCeO}}_2$

Ce compounds feature a remarkable diversity of electronic properties, which motivated extensive investigations over the last decades. Inelastic neutron scattering represents an important tool for understanding their underlying electronic structures but in certain cases a straightforward interpretation of the measured spectra is hampered by the presence of strong vibronic couplings. The latter may give rise to extra spectral features, which complicates the mapping of experimental data onto standard multiplet diagrams. To benchmark the performance of embedded-cluster quantum chemical computational schemes for the case of $4f$ systems, we here address the Ce $4f^1$ multiplet structure of $\mathrm{Na}\mathrm{Ce}{\mathrm{O}}_2$, an antiferromagnet with $D_{2d}$ magnetic-site symmetry for which neutron scattering measurements indicate only weak vibronic effects. Very good agreement with the experimental results is found in the computations, which validates our computational approach and confirms $\mathrm{Na}\mathrm{Ce}{\mathrm{O}}_2$ as a $4f$ magnet in the intermediate coupling regime with equally strong $4f$-shell spin-orbit and crystal-field interactions.

Figure 1

(a) Unit cell of $\mathrm{Na}\mathrm{Ce}{\mathrm{O}}_2$, plotted using the vesta visualization program [28]. Green, yellow, and red spheres indicate Ce, Na, and O species, respectively. (b) The 25-site cluster considered in the quantum chemical calculations. The crystalline environment (not depicted) was modeled as a large array of point charges in the computations.