FIG. 11.

Spinless NTOs for selected transitions between two quintet d⁶ states in a tris(pyrrolylmethyl)amine Fe(II) single-molecule magnet,²⁶³ which are responsible for its large (158 cm⁻¹) spin-reversal barrier. Q-Chem’s efficient EOM-CC implementation using the spin–orbit mean-field approximation and the Wigner–Eckart theorem enables calculations for medium-size molecules such as the one shown here. The computed spin-reversal barrier is within 1 cm⁻¹ of the experimental value.²⁵² The key object, the spinless triplet transition density matrix, provides valuable information about the nature of spin–orbit coupling and the related properties. Spinless NTOs (shown here) allow one to quantify and validate El-Sayed’s rules.²⁵² Reprinted with permission from Pokhilko et al., J. Phys. Chem. Lett. 10, 4857 (2019). Copyright 2019 American Chemical Society.