where E DFT represents the DFT energy and the rest is a dispersion correction. Only the C 6 and C 8 terms in Eq. ( ) are included in Grimme's popular D3 and D4 models, as higher-order terms are found to engender numerical problems while providing little improvement. Parameters s n ≤ 1 are functional-specific and the damping functions f n are chosen such that f n (R) → 0 faster than R n , so that the correction is damped to zero as R → 0. This has been called the "zero-damping" form of DFT+D, and that is the meaning of the notation DFT+D(0) in Eq. (2). Various damping functions f n have been considered. An alternative to D(0) damping is the "D(BJ)" correction scheme, first introduced by Becke and Johnson (BJ) in the context of the XDM model. In DFT+D(BJ), one corrects the DFT energy according to