The X40x10 Halogen Bonding Benchmark Revisited: Surprising Importance of (n-1)d Subvalence Correlation

Abstract

<p>We have re-evaluated the X40x10 benchmark for halogen bonding using conventional and explicitly correlated coupled cluster methods. For the aromatic dimers at small separation, improved CCSD(T)–MP2 “high-level corrections” (HLCs) cause substantial reductions in the dissociation energy. For the bromine and iodine species, (n-1)d subvalence correlation increases dissociation energies, and turns out to be more important for noncovalent interactions than is generally realized; ; (n-1)sp subvalence correlation is much less important. The (n-1)d subvalence term is dominated by core-valence correlation; with the smaller cc-pVDZ-F12-PP and cc-pVTZ-F12-PP basis sets, basis set convergence for the core-core contribution becomes sufficiently erratic that it may compromise results overall. The two factors conspire to generate discrepancies of up to 0.9 kcal/mol (0.16 kcal/mol RMS) between the original X40x10 data and the present revision.</p>

Non-Covalent Interactions Atlas Benchmark Data Sets 3: Repulsive Contacts

“…It had been shown earlier that these orbitals may contribute significantly to dispersion interactions. 11 This required the use of the polarizedcore variant of the basis sets from the aug-cc-pwCVXZ family. 12 Furthermore, to model the relativistic effects in these elements, the -PP variants of these basis sets were used along with the corresponding pseudopotentials.…”

Non-Covalent Interactions Atlas Benchmark Data Sets 2: Hydrogen Bonding in an Extended Chemical Space

“…23 Moreover, it has been shown that the sub-valence d orbitals on these atoms significantly contribute to dispersion interactions. 5 We have thus excluded these orbitals from the frozen core, which calls for the use of basis sets from the aug-cc-pwCVXZ-PP family. 24 All the interaction energies were calculated using counterpoise correction.…”

“…[2][3][4] Bromine and iodine are treated slightly differently in order to account for effects specific to heavier elements. 5 The complete protocol is outlined below; additional information can be found in the paper introducing the NCIA project. 1 In the NCIA project, special emphasis is placed on publishing the data sets openly in a form that simplifies their reuse.…”

Non-Covalent Interactions Atlas Benchmark Data Sets 5: London Dispersion in an Extended Chemical Space

“…17 In addition, the sub-valence d orbitals on these elements are excluded from the frozen-core approximation, as it had been shown that they may significantly contribute to dispersion interactions. 18 This requires a polarized-core variant of the basis sets, specifically from the aug-cc-pwCVXZ-PP series. 19 The resolution of identity approximation is applied in the calculation of correlation energy using the auxiliary basis sets optimized for the specific atomic orbital basis.…”