Description of reaction and vibrational energetics of CO₂–NH₃ interaction using quantum computing algorithms

CO₂ capture is critical to solving global warming. Amine-based solvents are extensively used to chemically absorb CO₂. Thus, it is crucial to study the chemical absorption of CO₂ by amine-based solvents to better understand and optimize CO₂ capture processes. Here, we use quantum computing algorithms to quantify molecular vibrational energies and reaction pathways between CO₂ and a simplified amine-based solvent model—NH₃. Molecular vibrational properties are important to understanding kinetics of reactions. However, the molecule size correlates with the strength of anharmonicity effect on vibrational properties, which can be challenging to address using classical computing. Quantum computing can help enhance molecular vibrational calculations by including anharmonicity. We implement a variational quantum eigensolver (VQE) algorithm in a quantum simulator to calculate ground state vibrational energies of reactants and products of the CO₂ and NH₃ reaction. The VQE calculations yield ground vibrational energies of CO₂ and NH₃ with similar accuracy to classical computing. In the presence of hardware noise, Compact Heuristic for Chemistry (CHC) ansatz with shallower circuit depth performs better than Unitary Vibrational Coupled Cluster. The “Zero Noise Extrapolation” error-mitigation approach in combination with CHC ansatz improves the vibrational calculation accuracy. Excited vibrational states are accessed with quantum equation of motion method for CO₂ and NH₃. Using quantum Hartree–Fock (HF) embedding algorithm to calculate electronic energies, the corresponding reaction profile compares favorably with Coupled Cluster Singles and Doubles while being more accurate than HF. Our research showcases quantum computing applications in the study of CO₂ capture reactions.