Berlin 2024 – scientific programme

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QI: Fachverband Quanteninformation

QI 27: Quantum Simulation II

QI 27.5: Talk

Thursday, March 21, 2024, 16:00–16:15, HFT-FT 101

MC-PDFT embedding scheme for electronic structure Quantum Algorithms — •Luca Righetti¹, Pauline Ollitrault^2,3, and Ivano Tavernelli² — ¹École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland — ²IBM Quantum, IBM Research Zurich, Rüschlikon, Switzerland — ³QC Ware, Palo Alto,CA,USA

In this work we propose a new hybrid quantum algorithm combining the Variational Quantum Eigensolver (VQE) algorithm with a classical embedding method. The embedding consists in employing Multiconfiguration Pair Density Functional Theory (MC-PDFT) theory as a post-processing method for calculating the final energy of the system. The hybrid algorithm is motivated by the need of properly treating electron correlation in strongly correlated systems. We also propose a self-consistently optimized version of VQE, where molecular coefficient are re-optimized after every iteration until convergence. By comparing the performance of our algorithm with classical methods having similar computational costs, we observe an improvement in the accuracy of dissociation energies and ground state energies of different molecules. We test our embedding method with H₂, H₂O and N₂. Our aim is not only to enhance the precision of VQE in predicting molecular energies, but also to reduce the depth and the width of the quantum circuit. Overall, this algorithm is able to achieve, in most cases, an accuracy comparable to more computationally expensive classical methods and to reduce quantum resources. We believe that this method can pave the way toward the simulation of larger molecular systems with current quantum devices.