Accurately modeling these magnetic systems remains a challenge for ab initio methods due to the large number of closely-lying electronic and spin states. This necessitates the use of multi-configuration methods, and the possible coupling between states through spin-orbit coupling requires relativistic effects to be considered. In this study we are targeting the former requirement using our LASSIS and LASSIS-PDFT method to investigate the spin state ordering and magnetic coupling for the tris-hydroxy-bridged chromium dimer, aka Kremer's dimer, depicted in Fig. . which are required to model superexchange processes, tends to increase the magnitude of the predicted coupling constant, as does including the effects of electron correlation involving nonmagnetic inactive orbitals as in the PT2 and PDFT results. The closest prediction to the experimental value is that of Sharma et al., for which a large active space (30,22) including ligand orbitals is employed in a PDFT energy calculation.