TDΔSCF: Time-Dependent Density Functional Theory with a Non-Aufbau Reference for Near-Degenerate States

-benzyne, and a more satisfactory description of bond dissociation without the spurious low-lying states found in SF-TDDFT. At the same time, the method exhibits a systematic tendency to overestimate singlet energies and can lose accuracy when the underlying ΔSCF reference is not well suited to the final state. We also identify a numerical instability that can arise in non-Aufbau calculations and trace its origin to the exchange-correlation potential near uncompensated nodal regions. These results highlight both the promise and the practical limitations of TDΔSCF as a low-cost method for singlet states with near-degenerate electronic structures.