Application of the Interacting Quantum Atoms Approach to the S66 and Ionic‐Hydrogen‐Bond Datasets for Noncovalent Interactions

Abstract

The interacting quantum atoms (IQA) method can assess, systematically and in great detail, the strength and physics of both covalent and noncovalent interactions. The lack of a pair density in density functional theory (DFT), which precludes the direct IQA decomposition of the characteristic exchange-correlation energy, has been recently overcome by means of a scaling technique, which can largely expand the applicability of the method. To better assess the utility of the augmented IQA methodology to derive quantum chemical decompositions at the atomic and molecular levels, we report the results of Hartree-Fock (HF) and DFT calculations on the complexes included in the S66 and the ionic H-bond databases of benchmark geometry and binding energies. For all structures, we perform single-point and geometry optimizations using HF and selected DFT methods with triple-ζ basis sets followed by full IQA calculations. Pairwise dispersion energies are accounted for by the D3 method. We analyze the goodness of the HF-D3 and DFT-D3 binding energies, the magnitude of numerical errors, the fragment and atomic distribution of formation energies, etc. It is shown that fragment-based IQA decomposes the formation energies in comparable terms to those of perturbative approaches and that the atomic IQA energies hold the promise of rigorously quantifying atomic and group energy contributions in larger biomolecular systems.

Interacting Quantum Atoms Approach and Electrostatic Solvation Energy: Assessing Atomic and Group Solvation Contributions

“…Its mean value is 0.76±1.36 kcal mol −1 , which corresponds to an average error per atom of 0.06±0.10 kcal mol −1 . The magnitudes of these error estimates are similar to those previously found in the IQA decomposition of formation energies for non‐covalent complexes . We note again that the actual interest of the IQA energy partitioning resides in the atomic and/or fragment‐based IQA components and they have values ranging from ∼0.5 to tens of kcal mol −1 in absolute value (see below) that are well above the mean numerical error per atom.…”

“…The IQA quantities are numerically integrated by PROMOLDEN over finite and irregular integration domains (i. e. atomic basins Ω A ) using angular and radial grids in atomic spherical quadratures that are much finer than those typically used by other QM software ,. We employed similar integration settings to those used in previous work and that represent a compromise choice between computational cost and accuracy for small and medium‐sized molecules. Thus, a β‐sphere around each atom was considered (i. e. a sphere completely contained inside the atomic basin), with a radius equal to 60 % the distance of its nucleus to the closest bond critical point in the electron density.…”

“…Thus, IQA provides self‐atomic energies, E (Ω A ), which tend to the free atomic energies at the limit of non‐interacting atoms, and diatomic E (Ω A, Ω B ) energies that unambiguously discriminate between classical electrostatic and exchange‐correlation energy terms. Using DFT (and HF) charge densities, IQA can be augmented with the Grimme's D3 potential, which yields pairwise dispersion energies E disp (A–B) that complement the diatomic E ( Ω A , Ω B ) IQA terms, constituting thus an effective D3‐IQA decomposition scheme applicable to medium‐sized and large systems. Hence, the IQA or D3‐IQA decomposition has been successfully applied to quantify many different aspects of chemical bonds and intermolecular forces.…”

“…Hence, the IQA or D3‐IQA decomposition has been successfully applied to quantify many different aspects of chemical bonds and intermolecular forces. Among the various topics that have been recently addressed using IQA, we find the nature and cooperativity of H‐bond interactions,− halogen bonding patterns, interactions within transition metal complexes,− description of short‐range repulsions, fine‐tuning effects of electron correlation within covalent and non‐bonded interactions, the categorization of non‐covalent bonding and the atomic decomposition of intermolecular binding energies, etc.…”

Interacting Quantum Atoms—A Review

“…In a systematic effort for validating the use of IQA energies for the study of non-covalent interactions, Suárez et al analysed the binding energies, magnitude of numerical errors, and the fragment and atomic distribution of formation energies within the IQA framework for the S66 and ionic-hydrogen-bond data sets. They shown that this energy partition rigorously quantify atomic and group energy contributions for biomolecular systems [ 88 ].…”