Applications of quantum simulation algorithms to obtain electronic energies of molecules on NISQ devices require careful consideration of resources for describing complex inter-electron correlation effects. In modeling these problems, the biggest challenge is posed by the fact that the number of qubits scales linearly with the size of molecular basis, which poses a significant limitation on the size of the basis sets and the number of correlated electrons included in quantum simulations of chemical processes. To address this issue and to enable more realistic simulations on near-term quantum computers, several algorithms have been proposed to effectively downfold correlation effects into the reduced-size orbital space, commonly referred to as the active space. Using downfolding techniques based on double unitary coupled-cluster (DUCC) Ansatz we demonstrate that the effect of the whole virtual orbitals space can be captured by small-size active spaces and by properly constructed active-space effective Hamiltonians. Combining the downfolding pre-processing technique with the Variational Quantum Eigensolver, we solve for the ground-state energy in the DUCC reduced active space and compare results to the configuration-interaction for Li2, H2, and HF.

Reducing wave-function complexity with DUCC using variational quantum algorithms on quantum computers

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.