Accurate Description of Intermolecular Interactions Involving Ions Using Symmetry-Adapted Perturbation Theory

Abstract

Three new data sets for intermolecular interactions, AHB21 for anion-neutral dimers, CHB6 for cation-neutral dimers, and IL16 for ion pairs, are assembled here, with complete-basis CCSD(T) results for each. These benchmarks are then used to evaluate the accuracy of the single-exchange approximation that is used for exchange energies in symmetry-adapted perturbation theory (SAPT), and the accuracy of SAPT based on wave function and density-functional descriptions of the monomers is evaluated. High-level SAPT calculations afford poor results for these data sets, and this includes the recently proposed "gold", "silver", and "bronze standards" of SAPT, namely, SAPT2+(3)-δMP2/aug-cc-pVTZ, SAPT2+/aug-cc-pVDZ, and sSAPT0/jun-cc-pVDZ, respectively [ Parker , T. M. , et al. , J. Chem. Phys. 2014 , 140 , 094106 ]. Especially poor results are obtained for symmetric shared-proton systems of the form X(-)···H(+)···X(-), for X = F, Cl, or OH. For the anionic data set, the SAPT2+(CCD)-δMP2/aug-cc-pVTZ method exhibits the best performance, with a mean absolute error (MAE) of 0.3 kcal/mol and a maximum error of 0.7 kcal/mol. For the cationic data set, the highest-level SAPT method, SAPT2+3-δMP2/aug-cc-pVQZ, outperforms the rest of the SAPT methods, with a MAE of 0.2 kcal/mol and a maximum error of 0.4 kcal/mol. For the ion-pair data set, the SAPT2+3-δMP2/aug-cc-pVTZ performs the best among all SAPT methods with a MAE of 0.3 kcal/mol and a maximum error of 0.9 kcal/mol. Overall, SAPT2+3-δMP2/aug-cc-pVTZ affords a small and balanced MAE (<0.5 kcal/mol) for all three data sets, with an overall MAE of 0.4 kcal/mol. Despite the breakdown of perturbation theory for ionic systems at short-range, SAPT can still be saved given two corrections: a "δHF" correction, which requires a supermolecular Hartree-Fock calculation to incorporate polarization effects beyond second order, and a "δMP2" correction, which requires a supermolecular MP2 calculation to account for higher-order induction-dispersion coupling. These corrections serve to remove artifacts introduced by the single exchange approximation in the exchange-induction and exchange-dispersion interactions, and obviate the need for ad hoc scaling of the first- and second-order exchange energies. Finally, some density-functional and MP2-based electronic structure methods are assessed as well, and we find that the best density-functional method for computing binding energies in these data sets is B97M-V/aug-cc-pVTZ, which affords a MAE of 0.4 kcal/mol, whereas complete-basis MP2 affords an MAE of 0.3 kcal/mol.

Accurate and Efficient Quantum Chemistry Calculations for Noncovalent Interactions in Many-Body Systems: The XSAPT Family of Methods

“…Parker et al 148 have proposed a "δMP2" correction, 29) to account for missing terms such as high-order coupling between induction and dispersion. This correction, which we find is especially important in ionic systems, 106 is equal to the difference between the counterpoise-corrected MP2 binding energy for the dimer and the SAPT2 binding energy. In XSAPT calculations, we apply the δE MP2 correction in a pairwise way, for dimers that include X − .…”

“…The single-exchange approximation is expected to be accurate at or beyond the van der Waals contact distance, 6 although problems for anionic systems necessitate some rescaling of the higher-order exchange interactions. 105,106 Neglecting intramolecular electron correlation but treating Vt o second order (the so-called SAPT0 approximation 9 ), we have Finally, it is common to incorporate polarization effects beyond second order by adding a correction term…”

Perspective: Found in translation: Quantum chemical tools for grasping non-covalent interactions

“…Generally, this approximation is very good, although it tends to break down for charged systems at close distances. [148][149][150] This failure can be overcome by scaling the exchange contribution 80 or by completely abandoning the S 2 approximation. 151 Overall, SAPT's lack of versatility remains perhaps its only true weakness.…”

Strength, character, and directionality of halogen bonds involving cationic halogen bond donors

“…26–28 The SAPT2+3δMP2/aTZ method has been shown to provide very accurate binding energies and is, among the family of SAPT techniques, among the optimal model chemistries for treating interactions between cations and anions. 29 All SAPT calculations are made using the Psi4 package. 30 …”

“…26–29 SAPT potential energy curves, as functions of intermolecular separation, as well as C-X…Cl − angles, are generated in order to investigate the factors influencing the strength and directionality of charged halogen bonds. The density functional-based, ωB97X-D/def2-TZVP/C-PCM method, incorporating an empirical dispersion function and an implicit solvation model, is used to investigate the effects that a salt’s solid-state medium might have on the strength of halogen bonds involving a cationic halogen bond donor and an anionic halogen bond acceptor.…”