These force fields also neglect the 8th-and 10th-order dispersion interactions. Quantumchemical calculations have shown that the C 8 dispersion term accounts for ca. 30% of the dispersion energy in both molecular dimers and in molecular crystals. The latter corresponds to roughly 20% of the computed lattice energies. A moderate increase in the magnitude of the C 6 dispersion terms can compensate for the neglect of higher-order terms, because these terms are much shorter-range than the 6th-order terms. Non-nonbonded potentials that include higher-order dispersion coefficients have been proposed in the past, but have not been widely adopted. The rigorous inclusion of higher-order dispersion terms in molecular-mechanical force fields may result in more accurate calculation of dispersion interactions and C 6 coefficients that are in better agreement with the experimental and XDM