Using LASSIS information in terms of 1-RDMs and 2-RDMs, we have demonstrated that LASSIS-PDFT is a straightforward and efficient method for incorporating electron correlation outside the active space, which is crucial for quantitative accuracy. We have shown that with LASSIS-PDFT, the energy gaps between different spin states for the [2Fe-2S] 2-dimer are significantly larger than for LASSIS, and the LASSIS-PDFT and DMRG-PDFT results for this system agree with each other at least as well and sometimes better than the LASSIS and DRMG references. LASSIS-PDFT also significantly improves over LASSIS in predicting the magnetic exchange interaction in the Kremer's dimer. Using LASSIS-PDFT, the spin-state gaps for the multimetallic systems AlFe 2 and Fe 3 were increased by up to three times compared to LASSIS.