A major shortcoming of the local density approximaton (LDA) and generalized gradient approximation (GGA) density functionals (with and without “exact exchange”) is their failure to properly describe long range correlation effects, such as dispersion forces. We present a novel atom-atom pairwise potential function for describing dispersion forces based the interaction of two spherical shells (of radius r_s) of polarizable media. The primary deviation from the C₆/R⁶ interaction of two point dipoles is due to the fact that atoms have volume. We will show that the resulting spherical atom potential: , is more accurate for describing dispersion interactions than either damped (radius r_d) or undamped C₆/R⁶ potentials, while not significantly affecting the computational cost of DFT methods. The spherical atom model for dispersion forces can also be incorporated into molecular mechanics force fields.