*3.8. Pristine Calixarenes–Molecular Properties*

Since in a further discussion the F-SAPT and SSMF3 methods will be employed for the analysis of intermolecular interactions, it is interesting to explore how the latter method reproduces first- and second-order molecular properties, such as electric dipole moments

and dipole polarizabilities. As discussed in the previous section, the HF and MP2 methods were selected for this test. For the CX case, the HF (MP2) dipole length is reproduced with the error of 6.6, −7.7, −1.9% (−13.5, −18, −16.5%) for the *pc*, *al*, and *wc* conformers, respectively, i.e., this property is reproduced with medium quality. However, the HF (MP2) average polarizability is reproduced with percent errors of 0.6, 1.4, and 3.2% (0.6, 1.5, 2.9%) for these conformers, respectively, which is a much better result. The average polarizability is a tensor invariant, but it is also interesting to examine off-diagonal terms in a given coordinate system since these terms are much smaller than diagonal terms and are more sensitive to applied approximations (see, e.g., the investigation of the influence of local approximations for static polarizabilities [104]). In particular, it is interesting to see whether the balancing of the fragmentation terms with plus and minus signs is accurate enough to reproduce zero or close-to-zero off-diagonal terms for the unfragmented molecule from possibly large (in terms of absolute values) off-diagonal terms for fragments. It turns out that this is indeed the case and, e.g., a small term *αxz* = −1.9 a.u. for the *al* conformer is reproduced as −1.3 a.u. as a summation of terms, which are individually as large as about ±30 a.u. Therefore, one can conclude that the molecular fragmentation model is useful for a semiqualitative reproduction of first-order molecular properties, while it behaves better for second-order properties if the third level of fragmentation is employed. It should be noted that nonbonded parts of the property were omitted here for the sake of simplicity. A full comparison of the dipole moment and polarizability components is presented in the Supplementary Information.
