Other works have used some form of the overlap of atomic densities to model Pauli repulsion while introducing only a few additional model parameters. While this would also align with the EDA representation of frozen repulsion, we found that this did not provide us with enough degrees of freedom to accurately match total energies. We owe this difficulty to the magnitude of E Pauli compared to E elec . In a point charge model, such as Amber99, the magnitude of the Pauli repulsion energy is more comparable to that of the electrostatic attraction and even dispersion energies. This is evident in Figure in which both E elec and E Pauli for the AMBER99 force field are both very much underestimated compared to the DFT values. However, in a model with electron overlap incorporated, this creates both an increase in intermolecular attraction from electrostatics, as well as an increase in Pauli repulsion due to the overlap itself. Hence while small changes to E Pauli 's profile as compared to only E Pauli itself may provide a sufficient fit, relative to the total energy E int , these differences can be quite large and sensitive to parameter adjustment.