We report on a reoptimization of the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential dedicated to the prediction of the band gaps of three-dimensional (3D) and layered hybrid organic-inorganic perovskites (HOPs) within pseudopotential-based density functional theory methods. These materials hold promise for future photovoltaic and optoelectronic applications. We begin by determining a set of parameters for 3D HOPs optimized over a large range of materials. Then we consider the case of layered HOPs. We design an empirical relationship that facilitates the prediction of band gaps of layered HOPs with arbitrary interlayer molecular spacers with a computational cost considerably lower than that of more advanced methods like hybrid functionals or $GW$. Our study also shows that substituting interlayer molecular chains of layered HOPs with Cs atoms is an appealing and cost-effective route to band gap calculations. Finally, we discuss the pitfalls and limitations of TB-mBJ for HOPs, notably its tendency to overestimate the effective masses due to the narrowing of the band dispersions. We expect our results to extend the use of TB-mBJ for other low-dimensional materials.

Kitaev magnets are materials with bond-dependent Ising interactions between localized spins on a honeycomb lattice. Such interactions could lead to a quantum spin-liquid (QSL) ground state at zero temperature. Recent theoretical studies suggest two potential signatures of a QSL at finite temperatures, namely, a scaling behavior of thermodynamic quantities in the presence of quenched disorder, and a two-step release of the magnetic entropy. Here, we present both signatures in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$ which is synthesized from $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ by replacing the interlayer Li atoms with Ag atoms. In addition, the dc susceptibility data confirm the absence of a long-range order, and the ac susceptibility data rule out a spin-glass transition. These observations suggest a closer proximity to the QSL in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$ compared to its parent compound $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ that orders at 15 K. We discuss an enhanced spin-orbit coupling due to a mixing between silver $d$ and oxygen $p$ orbitals as a potential underlying mechanism.

Searching for a Kitaev spin liquid phase motivated intense research on the honeycomb iridate materials. However, access to a spin liquid ground state has been hindered by magnetic ordering. ${\mathrm{Cu}}_2{\mathrm{IrO}}_3$ is a new honeycomb iridate without thermodynamic signatures of a long-range order. Here, we use muon spin relaxation to uncover the magnetic ground state of ${\mathrm{Cu}}_2{\mathrm{IrO}}_3$. We find a two-component depolarization with slow- and fast-relaxation rates corresponding to distinct regions with dynamic and static magnetism coexisting in the material. X-ray absorption spectroscopy and first-principles calculations identify a mixed copper valence as the origin of this behavior. Our results suggest that a minority of ${\mathrm{Cu}}^{2+}$ ions nucleate regions of static magnetism, whereas the majority of ${\mathrm{Cu}}^{+}/{\mathrm{Ir}}^{4+}$ on the honeycomb lattice give rise to a Kitaev spin liquid.

An initial investigation on the employment of targeted structural alterations, achieved through the post‐synthesis modification method, for modulation of the thermometric properties of metal–organic frameworks (MOFs) is reported. The MOF Eu_0.05Tb_0.95‐NBDC (NBDC = 2‐amino‐1,4‐benzenedicarboxylate) is chosen as pristine material, and its terminal N,N‐dimethylformamide (DMF) molecules are exchanged by various terminal and chelating ligands through a single‐crystal‐to‐single‐crystal coordinating solvent exchange reaction. Temperature‐dependence luminescence studies reveal that all samples are highly sensitive in the medium range with a maximum relative sensitivity of 2.6% K⁻¹ at 190 K for Eu_0.05Tb_0.95‐NBDC. In addition, a shift of 50 K of the operating temperature range is evidenced for the exchanged analogs. This is attributed to the occurrence of different deactivation pathways in the exchanged analogs due to the presence of N‐donor terminal or N/O‐donor chelating aromatic ancillary ligands in the place of DMF terminal ligands in the pristine material. Overall, this work provides insights into the role of terminal and chelating ligands on the thermometric properties of mixed Eu–Tb MOFs and proposes a promising strategy to control and modulate their thermometric performances.