Toward Quantitative Computations of Exchange Coupling Constants in Transition-Metal Complexes via Multireference Driven Similarity Renormalization Group

The
accurate prediction of magnetic exchange coupling constants
(J) in transition-metal complexes remains challenging
for the electronic-structure theory. In this work, we demonstrate
that the state-average driven similarity renormalization group second-order
perturbation theory (SA-DSRG-PT2), combined with the density matrix
renormalization group, provides quantitative J values
on a set of 21 3d bimetallic complexes with a focus on dicopper species.
Active orbitals are systematically identified using the atomic valence
active space approach, ensuring a consistent inclusion of metal 3d
and 4d shells and the ligand orbitals involved in superexchange pathways.
Analysis of the SA-DSRG-PT2 effective Hamiltonians indicates that
the reduction of the on-site Coulomb repulsion is the primary origin
of the improved exchange couplings. In addition, we adopt the orbital
mutual correlation plot as an intuitive tool to visualize exchange
pathways, allowing direct identifications of metal–metal and
metal–ligand correlations and their modulation by dynamical
correlation. These results establish SA-DSRG-PT2 as a robust and practical
multireference approach for studying magnetic interactions in transition-metal
complexes.