Here, the isotropic polarizability ᾱx for atom x is evaluated at imaginary frequency iω. In the D3 model, values for C 6,ab that depend on coordination numbers of atoms a and b are obtained by applying Eq. ( ) to model compounds, with polarizabilities computed using time-dependent (TD-)DFT. In the D4 model, these polarizabilities are further scaled based on Mulliken charges obtained from the SCF density, which provides additional dependence on the molecular environment. Higher-order C n coefficients, representing higher-order multipolar contributions to dispersion, can be approximated in terms of C 6 coefficients. The DFT+D3 and DFT+D4 models both incorporate Dobson's type-A nonadditivity (meaning C n coefficients that depend on the molecular environment) but neglect type-B nonadditivity (screening of the pairwise interactions by other polarizable centers). As a result, the pairwiseadditive approximations in Eqs. ( ) and (3) break down for larger molecules. To correct for this, an Axilrod-Teller-Muto (ATM) correction can be added, representing the leading-order contribution to three-body dispersion. In the D3 model, for example, this correction takes the form 36