The article presents a study of state-specific coupled-cluster (CC) methods for excited states, focusing on the ΔCCSD approach. ΔCCSD is a state-specific CC method that targets excited states using non-Aufbau determinants, particularly effective for doubly excited states where standard equation-of-motion CCSD (EOM-CCSD) is less accurate. The study compares ΔCCSD with EOM-CCSD and other high-level methods on a dataset of 276 excited states from the QUEST database, including doubly excited states, double–doublet transitions, and singly excited states of closed-shell systems. ΔCCSD generally performs well for doubly excited states, though it underperforms EOM-CCSD in some cases. For doublet–doublet transitions, the mean absolute errors (MAEs) of ΔCCSD and EOM-CCSD are 0.10 and 0.07 eV, respectively, with ΔCCSD showing slightly worse performance. This discrepancy is attributed to the multiconfigurational nature of some excited states, which are more challenging for ΔCCSD. The use of state-specific optimized orbitals typically improves accuracy. The study also evaluates the performance of ΔCCSD for open-shell singlet and triplet excited states, finding that it outperforms EOM-CCSD for doubly excited states but is less accurate for systems with multiple doubly excited determinants. The results indicate that ΔCCSD provides reasonable accuracy for many excited states, though it is not as precise as EOM-CCSD for certain cases. The use of optimized orbitals does not significantly improve accuracy compared to HF orbitals, suggesting that the method's performance is limited by the need to account for higher-order excitations. Overall, ΔCCSD is a viable alternative to EOM-CCSD for many excited states, particularly when state-specific orbitals are used.The article presents a study of state-specific coupled-cluster (CC) methods for excited states, focusing on the ΔCCSD approach. ΔCCSD is a state-specific CC method that targets excited states using non-Aufbau determinants, particularly effective for doubly excited states where standard equation-of-motion CCSD (EOM-CCSD) is less accurate. The study compares ΔCCSD with EOM-CCSD and other high-level methods on a dataset of 276 excited states from the QUEST database, including doubly excited states, double–doublet transitions, and singly excited states of closed-shell systems. ΔCCSD generally performs well for doubly excited states, though it underperforms EOM-CCSD in some cases. For doublet–doublet transitions, the mean absolute errors (MAEs) of ΔCCSD and EOM-CCSD are 0.10 and 0.07 eV, respectively, with ΔCCSD showing slightly worse performance. This discrepancy is attributed to the multiconfigurational nature of some excited states, which are more challenging for ΔCCSD. The use of state-specific optimized orbitals typically improves accuracy. The study also evaluates the performance of ΔCCSD for open-shell singlet and triplet excited states, finding that it outperforms EOM-CCSD for doubly excited states but is less accurate for systems with multiple doubly excited determinants. The results indicate that ΔCCSD provides reasonable accuracy for many excited states, though it is not as precise as EOM-CCSD for certain cases. The use of optimized orbitals does not significantly improve accuracy compared to HF orbitals, suggesting that the method's performance is limited by the need to account for higher-order excitations. Overall, ΔCCSD is a viable alternative to EOM-CCSD for many excited states, particularly when state-specific orbitals are used.