Abstract: In this talk, I will discuss our efforts in using density functional theory (DFT) for studying catalytic small-molecule activation in large systems. Specifically, we are interested in activation of the methane C-H bond to form methanol within the pores of zeolites as well as N₂ fixation by large actinide (5f) complexes. Catalytic methane-to-methanol conversion (MMC) is of great interest as methanol can be transported as a liquid and is a value-adding intermediate in the petrochemical industry.

Significant research has been focused on the issues surrounding the selectivity and yield of the MMC process on zeolitic materials. We have been interested in determining the suitability of DFT functionals for predicting the spin-state relative energies, reaction energies and barriers associated with MMC by zeolite-supported transition metal oxide (e.g., the spin-frustrated Cu₃O₃) cores. The effect of ​“heterobimetallicity” on the stability of the catalytic cores and the barrier for methane C-H activation will be discussed.

Despite these advances, the metal oxide cores implicated in MMC in zeolites, as well as the bis-actinide cores implicated in N₂ activation, have significant multiconfigurational characters. Thus, the utility of DFT for studying these systems is ultimately limited. To obtain quantitative results, we are developing a black-box, affordable multiconfigurational approach that is suited for studying catalytic small-molecule activation in these large systems. Specifically, we have extended the new multiconfigurational pair-density functional theory (MC-PDFT) to the quantum-mechanics/molecular mechanics ansatz. We have also implemented an automated scheme for selecting the active spaces used in the zeroth-order restricted active space self-consistent field solutions required for MC-PDFT.