Quantum mechanical method for the calculation of open-shell excited states. The method accurately describes low-lying multi-configurational electronic states of diradicals and triradicals in an efficient and robust single-reference scheme. The target low-spin states (e.g., S = 0 or S = 1/2) are described as spin-flipping excitations (S = −1) from a well-behaved high-spin reference state (e.g., S = 1 or S = 3/4). By employing theoretical models of increasing complexity for the reference (e.g., SCF
), the accuracy in the target states’ description can be systematically improved. The SF
methods result in multistate single-step computational schemes, e.g., several low-lying states can be computed in a single calculation that includes both dynamical and non-dynamical correlation effects.
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 427 (https://doi.org/10.1351/pac200779030293)