where s P is chosen so that the energy contribution of E Pauli at the Pauli "radii" R P contributes 1 kCal/mol. Other works have demonstrated that SAPT repulsive energies can be well approximated by a term proportional to either the overlap of the electron density or the wave functions of two different molecules. While it is certainly appealing to impose a connection between energy repulsion and the actual overlap of frozen densities ρ 0 , we have found that assigning each site it's own Pauli radii R P provided a better agreement between total model and QM energies (see section 4.3) due to the additional degrees of freedom to parameterize against. Only non-LP sites are used in the computation of Equation . To limit the number of parameters in the model, we do not use a unique exponent ζ P for each atomic site, but instead assign them on an element wise basis (H, C, N, and O).