Scaling up electronic structure calculations on quantum computers: The frozen natural orbital based method of increments

The method of increments and frozen natural orbital (MI-FNO) framework is introduced to help expedite the application of noisy, intermediate-scale quantum (NISQ) devices for quantum chemistry simulations. The MI-FNO framework provides a systematic reduction of the occupied and virtual orbital spaces for quantum chemistry simulations. The correlation energies of the resulting increments from the MI-FNO reduction can then be solved by various algorithms, including quantum algorithms such as the phase estimation algorithm and the variational quantum eigensolver (VQE). The unitary coupled-cluster singles and doubles VQE framework is used to obtain correlation energies for the case of small molecules (i.e., BeH2, CH4, NH3, H2O, and HF) using the cc-pVDZ basis set. The quantum resource requirements are estimated for a constrained geometry complex catalyst that is utilized in industrial settings for the polymerization of alpha-olefins. We show that the MI-FNO approach provides a significant reduction in the quantum bit (qubit) requirements relative to the full system simulations. We propose that the MI-FNO framework can create scalable examples of quantum chemistry problems that are appropriate for assessing the progress of NISQ devices. Published under an exclusive license by AIP Publishing.

Automated summary

The MI-FNO framework introduces the method of increments and frozen natural orbitals to expedite the application of NISQ devices for quantum chemistry simulations, reducing occupied and virtual orbital spaces systematically. By utilizing algorithms like VQE, it can solve correlation energies for small molecules effectively and significantly reduce quantum resource requirements. This approach creates scalable examples of quantum chemistry problems suitable for assessing NISQ device progress.