Separate from Grimme's D3 and D4 corrections, other formulations of DFT+D aim to incorporate type-A nonadditivity using the full SCF density rather than the density for a model compound or density-derived point charges. These alternatives include the XDM, MBD, and vdW-TS 51 dispersion corrections, each of which computes in situ C 6 coefficients in similar ways that take advantage of the relationship between polarizability and volume. Specifically, one may determine an effective atom-in-molecule polarizability for atom a (ᾱ eff a ), by scaling the free-atom polarizability ( ᾱfree a ) by a ratio equal to how the volume of a is compressed in its molecular environment: