We studied the electronic, magnetic, and optical properties of $\beta \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ insulator within the density-functional theory using the generalized gradient approximation taking into account strong Coulomb correlations (GGA+$U$) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The x-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Ir $L_{2,3}$ edges were investigated theoretically from first principles. The calculated results are in good agreement with experimental data. We found that the GGA+$U$ approach with Hubbard $U_{\text{eff}}=1.5\mathrm{eV}$ well describes the optical spectra and XMCD spectra at the Ir $L_{2,3}$ edges. We investigated the electronic structure of $\beta \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ under pressure from first principles. The hyperhoneycomb iridate $\beta \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ is on the border of the magnetic ordering with relatively weak Coulomb electron-electron correlations. The $\beta \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ undergoes a pressure-induced structural and magnetic phase transitions at $P_c=4.4$ GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by a dimerization of the previously equally long $x/y$ Ir-Ir bonds. We find remarkable nonmagnetic ground states of $\beta \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ at $P_c$, with a concomitant electronic phase transition from a Mott insulator to band insulators. We found that $J_{\text{eff}}=1/2$ states are still dominant in the low-energy region in high-pressure monoclinic $C2/c$ structure.

• Received 15 May 2018
• Revised 23 October 2018

DOI:https://doi.org/10.1103/PhysRevB.98.245113