Initial State Preparation of Ti-based Organometallic Polyolefin Catalyst using Clifford Circuits

The performance of quantum algorithms for ground-state energy estimation is impacted by the quality of the initial state. We present an efficient classical algorithm which prepares states that have significant overlap with the target eigenstate of a Hamiltonian and maps seamlessly into a quantum circuit. Our method uses a variant of the iterative qubit coupled cluster (iQCC) approach that exclusively uses Clifford circuits, and which, following the Gottesman–Knill theorem, scales polynomially on classical hardware. We further implement several optimizations to improve scalability to mitigate the exponential Hamiltonian growth incurred by the iQCC approach. The algorithm’s accuracy is first validated through ground-state simulations of small molecules such as H₂, LiH, and H₂O. We then extend the study to a more complex Ti-based organometallic complex, Ti(C₅H₅)(CH₃)₃, in a (20, 20) active space, requiring 40 qubits. Results demonstrate smooth convergence towards the reference energy, accurate ground-state representations, and circuits that can be further optimized for a quantum computer.