A Dynamically Weighted Constrained Complete Active Space Ansatz for Constructing Multiple Potential Energy Surfaces Within the Anderson-Holstein Model

We derive and implement the necessary equations for solving a dynamically weighted, state-averaged constrained CASSCF(2,2) wavefunction describing a molecule on a metal surface. We show that a partial constraint is far more robust than a full constraint. We further calculate the system-bath electronic couplings that arise because, near a metal, there is a continuum (rather than discrete) number of electronic states. This approach should be very useful for simulating heterogeneous electron transfer going forward.