Efficient evaluation of spin–orbit couplings in single-molecule magnets using DMRG within the DMET framework

The accurate characterization of complex electronic structures in single-molecule magnets (SMMs) is crucial for guiding their rational design. However, conventional multireference wavefunction theory faces significant computational bottlenecks for these systems, stemming from their intricate ligand environments and the necessity for large active spaces to capture strong electron correlation. To overcome these limitations, we introduce an efficient quantum embedding framework that synergistically combines density matrix embedding theory with ab initio density matrix renormalization group Relativistic spin-orbit coupling (SOC) effect is incorporated through a state-interaction procedure using the eXact two-component atomic mean-field spin-orbit (X2CAMF-SO) operator. Benchmarking on representative single-ion magnets confirms that our DMET-embedded DMRG-SI approach delivers results highly consistent with all-electron calculations, while offering a clear path for systematic improvement via active space expansion. Furthermore, by investigating SOC effects in a chromium dimer, we demonstrate the method's potential for high-accuracy and scalable ab initio studies of larger-sized polynuclear SMMs.