Coefficients C 8,ab can be obtained from the {C 6,a } computed for the MBD model. The SAPT(KS) + MBD method consists in adding the dispersion model of Eq. ( ) to the non-dispersion SAPT(KS) terms in Eq. ( ). XSAPT + MBD augments this with XPol charge embedding and uses LRCω GDD PBE to compute the monomer wavefunctions. Results in Fig. for the S66 dimers demonstrate that the accuracy of XSAPT + MBD is very similar to that of XSAPT + ai D3, without any three-body dispersion corrections, since type-B dispersion nonadditivity is insignificant for these small complexes. (See Table for the corresponding numerical data.) For the L7 complexes, however, XSAPT + MBD is appreciably more accurate than XSAPT + ai D3 even when a nonadditive dispersion correction is included in the latter (Fig. ). At present, XSAPT + MBD is the most accurate version of XSAPT, at least for charge-neutral complexes. (Performance for ions is discussed in Section 2.1.4.) Additional accuracy benchmarks are provided in Section 2.1 but we first introduce a few more aspects of the XSAPT methodology.