  The most advanced D-Wave Advantage quantum annealer has 5000+ qubits,
however, every qubit is connected to a small number of neighbors. As such,
implementation of a fully-connected graph results in an order of magnitude
reduction in qubit count. To compensate for the reduced number of qubits, one
has to rely on special heuristic software such as qbsolv, the purpose of which
is to decompose a large problem into smaller pieces that fit onto a quantum
annealer. In this work, we compare the performance of two implementations of
such software: the original open-source qbsolv which is a part of the D-Wave
Ocean tools and a new Mukai QUBO solver from Quantum Computing Inc. (QCI). The
comparison is done for solving the electronic structure problem and is
implemented in a classical mode (Tabu search techniques). The Quantum Annealer
Eigensolver is used to map the electronic structure eigenvalue-eigenvector
equation to a type of problem solvable on modern quantum annealers. We find
that the Mukai QUBO solver outperforms the Ocean qbsolv for all calculations
done in the present work, both the ground and excited state calculations. This
work stimulates the development of software to assist in the utilization of
modern quantum annealers.
