Large-Scale Quantum Computing Emulation for Accurate Triplet States of Ir(III) and Pt(II) Phosphorescent Emitters.

Predicting the phosphorescent emission gaps of heavy-metal complexes is crucial for organic light-emitting diode materials design, yet challenged by the highly entangled nature of their triplet states. Traditional projective single-reference methods like coupled cluster break down for these systems due to severe spin contamination, physically misidentifying the electronic character and yielding red-shifted gaps. The iQCC method executed on a classical computer emulates the fault-tolerant quantum simulation on the ∼200 logical qubit scale, to compute the energies of T1 and S0 for the phosphorescent complexes Ir(III) and Pt(II). iQCC achieves a mean absolute error of 0.05 eV and R2 of 0.94 relative to experiment, surpassing the approaches of DFT, TD-DFT, and coupled cluster. These results establish a high-accuracy performance target that molecular electronic-structure calculations on future fault-tolerant quantum computers should aim to exceed.