Absolutely Localized Multi-reference DFT Embedding

While density functional theory (DFT) has been a workhorse for quantum mechanical chemical calculations, current implementations have several deficiencies. Systems which require a multireference description are often poorly described by current DFT methods. Quantum embedding methods provide a strategy for performing localized highly accurate calculations on chemical systems while not incurring high cost computational scaling. Dividing a system into absolutely localized subsystems -- described by only the basis functions of the subsystem atoms -- can significantly reduce computational cost. The Huzinaga projection operator based absolute localization wavefunction embedded in DFT (WF-in-DFT) embedding methods match full system WF energy differences across a diverse test set including multi-reference WF calculations embedded in DFT. We have also studied large metal organic framework (MOF) cluster models, specifically gas adsorption on an Fe-MOF-74 cluster model and can achieve within 0.22 kcal/mol of the full system CASPT2 energy at a fraction of the computational cost. The absolute localization WF-in-DFT method allows for highly accurate calculations on multireference systems beyond the scope of current techniques.