Charge Transfer and Polarization in Force Fields: An Ab Initio Approach Based on the (Atom‐Condensed) Kohn–Sham Equations, Approximated by Second‐Order Perturbation Theory About the Reference Atoms (ACKS2)

After reviewing problematic cases for traditional fixed charge, atomic dipole‐polarized force fields, and machine‐learned model force fields, we discuss the ACKS2 (atom‐condensed Kohn–Sham equations; approximated at second order) alternative. ACKS2 provides an ab initio approach to force‐field development and solves some of the issues associated with previous electronegativity equalization methods for charge transfer and polarization. Some challenges for future researchers are mentioned.