Here, i and j are atom indices, ϵ is the dielectric constant, q i is the partial charge, d ij is the distance between atoms i and j, r i is the GB cavity radius for atom i, r solvent is the radius of water in the surface-area term, R i is the effective GB radius, f GB is the effective interaction distance and E SA is the surface area (SA) energy scale (2.26 kJ/mol/nm 2 ). The SA term in Eq (1c) is a modified version of Eq (2) from Schaefer et al. that is implemented in OpenMM, which is different from the SA terms implemented in the AMBER program. The effective interaction distance is given by 39