Spin-State Ordering in Metal-Based Compounds Using the Localized Active Space Self-Consistent Field Method. 
Quantitatively accurate calculations for spin-state ordering in transition-metal complexes typically demand a robust multiconfigurational treatment.  The poor scaling of such methods with increasing size makes them impractical for large, strongly correlated systems.  Density matrix embedding theory (DMET) is a fragmentation approach that can be used to specifically address this challenge.  The single-determinantal bath framework of DMET is applicable in many situations, but it has been shown to perform poorly for molecules characterized by strong correlation when a multiconfigurational self-consistent field solver is used.  To ameliorate this problem, the localized active space self-consistent field (LASSCF) method was recently described.  In this work, LASSCF is applied to predict spin-state energetics in mono- and di-iron systems, and we show that the model offers an accuracy equivalent to that of CASSCF but at a substantially lower computational cost.  Performance as a function of basis set and active space is also examined.