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The random phase approximation (RPA) has received a considerable interest in the field of modeling systems where noncovalent interactions are important. Its advantages over widely used density functional theory (DFT) approximations are the exact treatment of exchange and the description of long-range correlation. In this work we address two open questions related to RPA. First, how accurately RPA describes nonadditive interactions encountered in many-body expansion of a binding energy. We consider three-body nonadditive energies in molecular and atomic clusters. Second, how does the accuracy of RPA depend on input provided by different DFT models, without resorting to selfconsistent RPA procedure which is currently impractical for calculations employing periodic boundary conditions. We find that RPA based on the SCAN0 and PBE0 models, i.e., hybrid DFT, achieves an overall accuracy between CCSD and MP3 on a dataset of molecular trimers of Řezáč et al. (J. Chem. Theory. Comput. 2015, 11, 3065) Finally, many-body expansion for molecular clusters and solids often leads to a large number of small contributions that need to be calculated with a high precision. We therefore present a cubic-scaling (or SCF-like) implementation of RPA in atomic basis set, which is designed for calculations with a high numerical precision. rors originating from the exchange functional are on the same order as the errors originating from the missing dispersion energy. [19][20][21] Approximate exchange functionals alone can lead to both strongly overestimated and underestimated noncovalent interactions. 22 For two body systems such issues tend to be masked by adjusting the equilibrium-and short-distance behavior of the dispersion correction. 19 However, the three-body exchange errors cannot be compensated in a similar way by adjusting the pairwise additive dispersion corrections. 19 Overall, the conclusion originating from the existing literature is that no existing semilocal functional can reliably account for many body effects. 21,23 Affordable schemes based on perturbation theory could offer higher and systematically improvable accuracy for calculations of condensed systems compared to standard DFT functionals. 21,[24][25][26][27] Of such schemes, the random phase approximation to the correlation energy (RPA) is promising as it is both compatible with the Hartree-Fock (HF) exchange and it contains terms describing higher-order (nonadditive) correlation effects. 28,29 RPA has been tested for interaction energies of dimers, 30-32 for adsorption, [33][34][35] or for molecular 36-39 and atomic solids 40 and interfaces. 41,42 For the cases involving noncovalent interactions, high accuracy has been achieved with addition of the singles corrections. 43,44 However, its accuracy for predicting nonadditive energies is unknown and this is one of our interests in this work. Moreover, most of the RPA calculations nowadays are performed non-self-consistently, using DFT orbitals and energies in the RPA energy expression. Here we obtain RPA results usi...

Intermolecular ternary complexes composed of: (1) the centrally placed trifluoroacetonitrile or its higher analogs with central carbon exchanged by silicon or germanium (M = C, Si, Ge), (2) the benzonitrile molecule or its para derivatives on one side, and (3) the boron trifluoride of trichloride molecule (X = F, Cl) on the opposite side as well as the corresponding intermolecular tetrel- and triel-bonded binary complexes, were investigated by symmetry-adapted perturbation theory (SAPT) and the supermolecular Møller-Plesset method (MP2) at the complete basis set limit for optimized geometries. A character of interactions was studied by quantum theory of atoms-in-molecules (QTAIM). A comparison of interaction energies and QTAIM bond descriptors for dimers and trimers reveals that tetrel and triel bonds increase in their strength if present together in the trimer. For the triel-bonded complex, this growth leads to a change of the bond character from closed-shell to partly covalent for Si or Ge tetrel atoms, so the resulting bonding scheme corresponds to a preliminary stage of the SN2 reaction. Limitations of the Lewis theory of acids and bases were shown by its failure in predicting the stability order of the triel complexes. The necessity of including interaction energy terms beyond the electrostatic component for an elucidation of the nature of σ- and π-holes was presented by a SAPT energy decomposition and by a study of differences in monomer electrostatic potentials obtained either from isolated monomer densities, or from densities resulting from a perturbation with the effective field of another monomer.