  A widely used strategy to reduce the computational cost in quantum-chemical
calculations is to partition the system into an active subsystem, which is the
focus of the computational efforts and an environment that is treated at a
lower computational level. The system partitioning is mostly based on localized
molecular orbitals. When reaction paths or energy differences are to be
calculated, it is crucial to keep the orbital space consistent for all
structures. Inconsistencies in the orbital space can lead to unpredictable
errors in the potential energy surface. While successful strategies to ensure
this consistency have been established for organic and even metal-organic
systems, these methods often fail for metal clusters or nanoparticles with a
high density of near-degenerate and delocalized molecular orbitals. However,
such systems are highly relevant for catalysis. Accurate yet feasible
quantum-mechanical ab initio calculations are therefore highly desired. In this
work, we present an approach based on the SPADE algorithm that allows us to
ensure an automated and consistent partitioning even for systems with
delocalized and near-degenerate molecular orbitals and demonstrate the validity
of this method for the binding energies of small molecules on transition-metal
clusters.
