Controlling Molecular Structure and Spin with Multiconfigurational Quantum Chemistry

B. Vlaisavljevich, University of South Dakota (Principal Investigator)

The goal of this work is to develop software to understand how one might control the changes in molecular structure that are induced by changes in the electronic spin state. The work is particularly aimed at transition metal complexes with notoriously challenging electronic structures including spin-crossover complexes, metalloporphyrins, and metallocorroles. The research will focus on three objectives: Improving structural control in spin-crossover complexes, providing mechanistic insights in catalysis, and controlling spin with external stimuli. Efforts in this field to date have studied changes in molecular structures using density functional theory (DFT).  Studies with higher-level calculations have focused only on fixed structures or isolated geometric changes. Traditional analysis assumes that the molecular structure is well-described with DFT for many cases even when the electronic structure is not. This work will test that assumption by performing full geometry optimizations with the complete active space perturbation theory (CASPT2) method, making use of newly implemented, fully internally contracted analytical nuclear gradients. Moreover, these calculations are made feasible for transition metal complexes through the parallel BAGEL program package’s ability to exploit modern high performing computing resources. Subtle but important changes in geometry are likely to be identified for molecular complexes of interest for use as sensors, catalysts, and in molecular electronics.