Automatic Algorithm Switching for Accurate Quantum Chemical Calculations

Abstract

Quantum chemical calculations (QCC) are computational techniques to analyze the characteristics of molecules. The variational quantum eigensolver (VQE) designed for noisy intermediate-scale quantum (NISQ) computers can be used to calculate the ground-state energies of molecules, while coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] is regarded as a traditional gold standard algorithm in QCC. The advantage between CCSD(T) and VQE in terms of the accuracy of ground-state energy calculation differs depending on molecular structures. In this work, we propose an automatic algorithm switching (AAS) technique to accurately calculate the ground-state energies of a target molecule with different bond distances. It automatically switches CCSD(T) and VQE by identifying a bond distance where the accuracy of CCSD(T) begins to drop for a target molecule. Our evaluation using a noise-less quantum computer simulator demonstrates that AAS improves the accuracy to describe the bond breaking processes of molecules compared to CCSD(T) and VQE.