Estimating Phosphorescent Emission Energies in Ir^III Complexes Using Large‐Scale Quantum Computing Simulations**

Abstract

Here we calculate T1→S0 transition energies in nine phosphorescent iridium complexes using the iterative qubit coupled cluster (iQCC) method to determine if quantum simulations have any advantages over classical methods. These simulations would require a gate‐based quantum computer with at least 72 fully‐connected logical qubits. Since such devices do not yet exist, we demonstrate the iQCC method using a purpose‐built quantum simulator on classical hardware. The results are compared to a selection of common DFT functionals, ab initio methods, and empirical data. iQCC is found to match the accuracy of the best DFT functionals, but with a better correlation coefficient, demonstrating that it is better at predicting the structure–property relationship. Results indicate that the iQCC method has the required accuracy to design organometallic complexes when deployed on emerging quantum hardware and sets an industrially relevant target for demonstrating quantum advantage.

Perspective on the Current State-of-the-Art of Quantum Computing for Drug Discovery Applications

“…An important part of that is the ability to give better results than DFT at a reasonable cost. Recent work on photochemical processes with simulated quantum computing uses precisely such criteria . Unfortunately, the assessment of potential quantum benefit for pharma remains a difficult task, not in the least because predictive application of quantum mechanics in the drug discovery process is a relatively new trend even using classical computers .…”

“…For strongly correlated systems, the main difficulty lies in the size of the active spaces required for correctly describing some systems, an area where quantum computers may make a breakthrough. 41 For weakly correlated systems, high-quality results delivered by quantum computers may still yield significant improvements over popular density functional theory (DFT) approaches 42 or even efficient wave function based approaches on the classical computer.…”

“…Recent work on photochemical processes with simulated quantum computing uses precisely such criteria. 42 Unfortunately, the assessment of potential quantum benefit for pharma remains a difficult task, not in the least because predictive application of quantum mechanics in the drug discovery process is a relatively new trend even using classical computers. 3 Some areas where quantum effects are known to be important, such as the description of weak hydrogen bonds, 44 also stand out as the most likely candidates for quantum benefit.…”

Growth Reduction of Similarity-Transformed Electronic Hamiltonians in Qubit Space

“…Following optimization of the generators’ associated variational amplitudes, the unitary is used to transform the current step Hamiltonian in the qubit space. The iQCC method has demonstrated systematic convergence toward ground state and excited state energies for problems requiring up to 72 logical qubits. , Furthermore, a posteriori corrections have been developed to further increase the accuracy of iQCC energy estimates . The employed Hamiltonian transformations are exact, where formally all BCH terms are summed in acquiring Ĥ eff with no neglecting of high body fermionic terms.…”

“…Hence, while iQCC is a formally variational unitary downfolding procedure, the effective iQCC Hamiltonians have demonstrated a rapid increase in the number of terms, particularly accentuated for the initial iterations. It has been elucidated that the rate of Pauli product increase diminishes at later iterations . Nevertheless, the main computational expense of the iQCC procedure arises from the introduction of a prohibitive number of Pauli products in the iQCC effective Hamiltonians.…”