The electrostatic energy in Eq. ( ) differs from and simplifies the well-known Kirkwood expression in two ways: (i) the charges in the protein interior are not dissociated and the position of the charges is thus confined to the surface of the dielectric discontinuity; and (ii) the charges are not point-like but have a finite angular size described through a normal distribution on the sphere, quantified by the parameter λ . In addition, Kirkwood and Shumaker consider the electrostatic interactions either only through the electrostatic self-energy or neglect them altogether.