posted on 2024-03-14, 18:40authored byEnhua Xu, Yuma Shimomoto, Seiichiro L. Ten-no, Takashi Tsuchimochi
In
this work, we utilize the framework of many-body expansion (MBE)
to decompose electronic structures into fragments by incrementing
virtual orbitals, aiming to accurately solve the ground and excited
state energies of each fragment using the variational quantum eigensolver
and deflation algorithms. While our approach is primarily based on
unitary coupled cluster singles and doubles (UCCSD) and its generalization,
we also introduce modifications and approximations to conserve quantum
resources in MBE by partially generalizing the UCCSD operator and
neglecting the relaxation of the reference states. As a proof of concept,
we investigate the potential energy surfaces for the bond-breaking
processes of the ground state of two molecules (H2O and
N2) and calculate the ground and excited state energies
of three molecules (LiH, CH+, and H2O). The
results demonstrate that our approach can, in principle, provide reliable
descriptions in all the tests including strongly correlated systems
when appropriate approximations are chosen. Additionally, we perform
model simulations to investigate the impact of shot noise on the total
MBE energy and show that precise energy estimation is crucial for
lower-order MBE fragments.