The XDM method was found to provide molecular C 6 dispersion coefficients that are in good agreement with the experimental values. Evaluation of the XDM dispersion coefficients and dispersion energy can be performed routinely from a ground-state density-functional theory (DFT) calculation using standard quantum-chemistry codes. The calculation of atomic London dispersion coefficients using XDM could provide an innovative method to validate force-field dispersion parameters. Molecular dynamics simulations of organic molecules often employ a generalized molecularmechanical force field. These force fields define parameters for the standard types of chemical bonds and functional groups present in organic molecules, making it possible to generate a force field automatically for an arbitrary molecule. CGenFF, 27 GAFF, and OPLS 29 are popular generalized force fields. More recently, models that are capable of describing induced polarization, such as Drude polarizable force fields, have also been developed. The CGenFF, GAFF, OPLS, and Drude force fields all account for inter-atomic London dispersion interactions via the Lennard-Jones 12-6 potential. This potential combines the attractive 1/r London dispersion term with a 1/r 12 short-range repulsive term. The components of this potential are illustrated in Figure . Higher order dispersion terms (i.e., C 8 and C 10 ) are neglected. The Lennard-Jones potential for the interaction between atoms i and j is