Constrained CASSCF: Probing Charge-Transfer and Non-Adiabatic Dynamics at Ground State Cost

We present a novel method for investigating charge transfer states and D1-D0 crossings for systems with odd numbers of electrons. By enforcing equal projection of active orbital subspaces onto donor and acceptor fragments, this approach enables efficient characterization of charge transfer processes via CASSCF with minimal active space. With an optimized algorithm, the method allows for speedy non-adiabatic dynamics simulations at computational costs comparable to Born-Oppenheimer molecular dynamics.