MP2-IQA: upscaling the analysis of topologically partitioned electron correlation

Abstract

When electronic correlation energy is partitioned topologically, a detailed picture of its distribution emerges, both within atoms and between any two atoms. This methodology allows one to study dispersion beyond its more narrow definition in long-range Rayleigh-Schrödinger perturbation theory. The interacting quantum atoms (IQA) method was applied to MP2/6-31G(d,p) (uncontracted) wave functions of a wide variety of systems: glycine…water (hydration), the ethene dimer (π-π interactions), benzene (aromaticity), cyclobutadiene (antiaromaticity), and NH3BH3 (dative bond). Through the study of molecular complexes it turns out that dispersion energy is either important to a system’s stabilization (for the C2H4 dimer) or not important (for Gly…H2O). We have also discovered that the delocalization in benzene lowers the strength of Coulomb repulsion in the bonds, which has been quantified for the first time through IQA. Finally, we showed that the nature of the dative bond is much different from that of a regular covalent bond as it is not destabilized by electronic correlation. Finally, the conclusions obtained for these archetypical systems have implications for the future of the quantum topological force field FFLUX in the simulation of larger systems. Graphical abstractAtomic and bond dynamic correlation energies are now available thanks to IQA. Larger molecules can now be accessed to include resonance and solvation of FFLUX force field Electronic supplementary materialThe online version of this article (10.1007/s00894-018-3717-5) contains supplementary material, which is available to authorized users.

Atomic Partitioning of the MPn (n = 2, 3, 4) Dynamic Electron Correlation Energy by the Interacting Quantum Atoms Method: A Fast and Accurate Electrostatic Potential Integral Approach

“…) over the grid that does not include the DO‐loops. This large number of DO‐loops has confined the application of to small systems only, with some of our larger systems studied being the water pentamer, glycine and glycine…water …”

“…Much later, the first IQA‐partitioned electron correlation energies were computed in the context of coupled cluster theory, coupled‐cluster Lagrangian densities and CCSD(T) wave functions . Very recently, we carried out IQA‐MPn for the first time, applied it to the machine learning method Gaussian Process Regression (also known as kriging), quantified electron correlation of the chemical bond (showing that ionicity and covalency are not each other's opposite), demonstrated the transferability of topologically partitioned electron correlation energies in water clusters, studied the effects of higher orders of perturbation theory on the correlation energy of atoms and bonds in molecules, and finally calculated dynamic electron correlation in a wider variety of systems including glycine…water (hydration), the ethene dimer (π–π interactions), benzene (aromaticity), cyclobutadiene (antiaromaticity), and NH 3 BH 3 (dative bond).…”

Contributions of IQA electron correlation in understanding the chemical bond and non-covalent interactions

“…The details of our approach have been exhaustively explained in previous publications [32,[41][42][43][44][45]. The IQA method has been developed for over two decades, and was initially applied mainly at Hartree-Fock level [31], but was more recently made compatible with density functional theory [38,46,47].…”

“…The detailed formalism and the equations involved in IQA will be introduced in the next section. As an example of how naturally IQA handles dispersion wherever it occurs (intramolecular or intermolecular) we have recently [32] shown that a non-covalent C...H interaction in monomeric glycine has a dispersive interaction of −0.3 kJ mol −1 . This value is very similar to the C...H electron correlation energy associated with a carbon and a hydrogen interacting through-space from different molecules in the ethylene dimer (−0.4 kJ mol −1 ).…”

Interacting Quantum Atoms—A Review

“…The IQA partition combined with the MP2 approximation was successfully used for the first time by Popelier and coworkers to study electron correlation [ 40 , 41 ]. The problem with this initial IQA/MP2 approach is that its computational cost is practically the same as the one corresponding to an IQA/CCSD partition.…”