Surface reaction calculations with quantum computers for battery materials

Abstract

Understanding electronic behaviour via quantum chemistry calculations is useful for various applications. But solving the many-body Schrödinger equation exactly is unfeasible due to complex interactions between electrons. Density Functional Theory (DFT) is immensely powerful, but it struggles with certain types of electron correlations. Quantum Computing offers a promising alternative, especially in scenarios with highly localised electrons, such as in surface reactions. In our previous work, we developed a quantum embedding technique for efficiently simulating surface reactions in quantum computers. While most of the orbitals are treated classically, the most relevant (i.e. the active space) orbitals are processed in the quantum computer. In the present work, we apply this specialised embedding method to the Oxygen reduction reaction at the surface of Lithium battery electrodes. The quantum calculations employ methods such as ADAPT-VQE, Entanglement Forging and the Local Unitary Cluster Jastrow (LUCJ) ansatz for building efficient quantum circuits optimized for near-term quantum devices. We tackle the Schrödinger equation within the active space using the Variational Quantum Eigensolver (VQE), which involves evaluating the expectation value of the active-space Hamiltonian over a quantum circuit. We compare two methods for ranking and selecting active-space orbitals, which are based on the impact of each orbital on the ground-state energy and their contribution to the electronic density changes from pre- to post-reaction configurations. As a result, we obtain the reaction energy difference within chemical accuracy with respect to CCSD calculations, showing that this methodology holds promise for advancing the understanding of Li-O2 surface interactions.