Estimating Phosphorescent Emission Energies in Ir(III) Complexes using Large-Scale Quantum Computing Simulations

Quantum chemistry simulations that accurately predict the properties of materials are among the most highly anticipated applications of quantum computing. It is widely believed that simulations running on quantum computers will allow for higher accuracy, but there has not yet been a convincing demonstration that quantum methods are competitive with existing classical methods at scale. Here we apply the iterative qubit coupled cluster (iQCC) method on classical hardware to the calculation of the $T_1 \to S_0$ transition energies in nine phosphorescent iridium complexes, to determine if quantum simulations have any advantage over traditional computing methods. Phosphorescent iridium complexes are integral to the widespread commercialization of organic light-emitting diode (OLED) technology, yet accurate computational prediction of their emission energies remains a challenge. Our simulations would require a gate-based quantum computer with a minimum of 72 fully-connected and error-corrected logical qubits. Since such devices do not yet exist, we demonstrate the iQCC quantum method using a special purpose quantum simulator on classical hardware. The results are compared to a selection of common density-functional theory (DFT) functionals (B3LYP, CAM-B3LYP, LC-wHPBE), ab initio methods (HF and MP2), and experimental data. The iQCC quantum method is found to match the accuracy of the fine-tuned DFT functionals, has a better Pearson correlation coefficient, and still has considerable potential for systematic improvement. Based on these results, we anticipate that the iQCC quantum method will have the required accuracy to design organometallic complexes when deployed on emerging quantum hardware.