Corresponding Active Orbital Spaces along Chemical Reaction Paths

The accuracy of reaction
energy profiles calculated with multiconfigurational
electronic structure methods and corrected by multireference perturbation
theory depends crucially on consistent active orbital spaces selected
along the reaction path. However, it has been challenging to choose
molecular orbitals that can be considered corresponding in different
molecular structures. Here, we demonstrate how active orbital spaces
can be selected consistently along reaction coordinates in a fully
automatized way. The approach requires no structure interpolation
between reactants and products. Instead, it emerges from a synergy
of the Direct Orbital Selection orbital mapping ansatz combined with
our fully automated active space selection algorithm autoCAS. We demonstrate our algorithm for the potential energy profile of
the homolytic carbon–carbon bond dissociation and rotation
around the double bond of 1-pentene in the electronic ground state.
However, our algorithm also applies to electronically excited Born–Oppenheimer
surfaces.