Identify the source of the residual interaction-energy error in direct QSCI

Identify whether the large positive residual interaction energy produced by direct QSCI for the CAS(12e,12o) benzene dimer arises from limitations in the prepared quantum state, the selected determinant space, or other differences between the computational workflows.

Background

Direct QSCI yields a residual interaction energy of approximately +24.56 kcal/mol at a separation of 6.0 Å, even though the interaction should vanish asymptotically. The authors note that direct QSCI and Deep QSCI also use different state-preparation ansätze and active spaces, making the source of the discrepancy difficult to isolate.

The paper explicitly states that the available data do not determine the cause, leaving the origin of the direct-QSCI error unresolved.

References

This large residual value limits a quantitative interpretation of the direct QSCI results and may reflect limitations in the prepared state or the selected determinant space. The present data do not identify the cause.

— A Divide-and-Conquer Quantum-Selected Configuration Interaction for Evaluating $π$-$π$ Stacking Interaction Energies in the Benzene Dimer  (2609.36708 - Tajima et al., 29 Sep 2026) in Section 5, Results