Size-consistency and orbital-invariance issues revealed by VQE-UCCSD calculations with the FMO scheme

Abstract

The fragment molecular orbital (FMO) scheme is one of the popular fragmentation-based methods and has the potential advantage of making the circuit flat in quantum chemical calculations on quantum computers. In this study, we used a GPU-accelerated quantum simulator (cuQuantum) to perform the electron correlation part of the FMO calculation as unitary coupled-cluster singles and doubles (UCCSD) with the variational quantum eigensolver (VQE) for hydrogen-bonded (FH)${}_3$ and (FH)${}_2$-H${}_2$O systems with the STO-3G basis set. VQE-UCCD calculations were performed using both canonical and localized MO sets, and the results were examined from the point of view of size-consistency and orbital-invariance affected by the Trotter error. It was found that the use of localized MO leads to better results, especially for (FH)${}_2$-H${}_2$O. The GPU acceleration was substantial for the simulations with larger numbers of qubits, and was about a factor of 6.7--7.7 for 18 qubit systems.

20 + 3 pages, 3 + 2 figures, 5 + 3 tables

References in corpus (2)

• Simulated Quantum Computation of Molecular Energies
• Chemical Basis of Trotter-Suzuki Errors in Quantum Chemistry Simulation

Cited by in corpus (1)

• Does the full configuration interaction method based on quantum phase estimation with Trotter decomposition satisfy the size consistency condition?