Density Matrix Embedding Pair-Density Functional Theory for Molecules

We combine density matrix embedding theory (DMET) with multiconfiguration pair-density functional theory (MC-PDFT) to explore finite systems exhibiting localized strong electron correlation effects. This methodology, termed density matrix embedded pair-density functional theory (DME-PDFT), provides a substantial cost reduction compared to traditional nonembedded MC-PDFT. Additionally, we compare it with second order n-electron valence state perturbation theory within DMET (NEVPT2-DMET). We have validated these methods by computing the bond dissociation in methyl diazine and spin-splitting energy gap in the [Fe(H₂O)₆]²⁺ complex, showing that DME-PDFT splitting energies converge faster compared to NEVPT2-DMET to the corresponding nonembedding limits. We finally compare embedding schemes with truncation schemes for two extended transition metal complexes, Fe[N(H)Ar*]₂ and [NiC₉₀N₂₀H₁₂₀]²⁺, and show that embedding schemes are more accurate than truncations when the transition metal is not fully coordinated.