A Quantum-HPC Hybrid Workflow for Reaction-Center Electronic Dynamics: Application to a Cytochrome P450-Inspired Iron-Complex Model

We introduce population-transfer dynamics as a practical validation observable for active-state-derived reduced Hamiltonians in multistate reaction-center chemistry. In transition-metal systems, missing couplings or configurations can compromise the reliability of reduced active space models along a reaction coordinate, even when the overall spectrum is reproduced reasonably well. Using a cytochrome P450-inspired Fe-complex model, we construct a reaction-coordinate-dependent effective Hamiltonian from state-averaged complete active-space self-consistent field (SA-CASSCF) calculations, map it to a quantum circuit representation suitable for current hardware, and propagate the dynamics from the reactant-side ground state. At the spectrum level, the reduced Hamiltonian reproduces the SA-CASSCF reference with an RMS deviation of 0.030 eV and a maximum absolute deviation of 0.143 eV. As a dynamics-based diagnostic, the product-manifold population pP(t) identifies a pronounced near-degeneracy window around x ≈ 0.3, where state mixing is strongest; specifically, computed from classical exact time evolution reaches 0.488 at x = 0.3 after 10 fs, compared with 7.26 × 10-2 at x = 0.2 and 5.90 × 10-3 at x = 0.0. To render the workflow executable on current trapped-ion hardware, we quantify the NISQ-relevant trade-off between dynamical fidelity and circuit resources through coupling pruning and first-order Trotterization. A coupling cutoff of ε = 0.02 eV reduces the nonzero coupling set from 32 to 7 while preserving the dominant transfer pathways, and a Trotter step number of M = 30 provides the best practical operating point among the tested values. Finally, we demonstrate the end-to-end workflow on Quantinuum's trapped-ion quantum computer Reimei. The hardware reproduces the key reaction-coordinate trend identified by the classical reduced model, including the pronounced maximum at x = 0.3, where the measured product population is 0.42 on hardware and 0.43 on the matched emulator. Overall, this work establishes a dynamics-based diagnostic route for assessing the adequacy of active-space-derived reduced Hamiltonians and shows that chemically interpretable multistate electronic dynamics can already be executed on current trapped-ion hardware under realistic device constraints.