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

Paul L A Popelier,Arnaldo F Silva

doi:10.1007/s00894-018-3717-5

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

Highlights

Obtaining meaningful electronic correlation energy (ECE) and dispersion energy continues to be a priority in the electronic structure community
Investigating bond electronic correlation energies is more intricate than investigating atomic correlation energies because they are second in magnitude compared to intra-atomic correlation and their sign is sensitive to the nature of the bond
Pendás et al [15] carried out an interacting quantum atoms (IQA) electron correlation analysis of several systems, but they used CCSD(T) densities

Summary

Introduction

Obtaining meaningful electronic correlation energy (ECE) and dispersion energy continues to be a priority in the electronic structure community. Density functional theory (DFT) methods can benefit from the development of electronic correlation methods because dispersion corrections in DFT is. As far as our knowledge goes, it was only recently that anyone reported the ability to calculate ECEs for a MPn wave function within the IQA formalism. This capability was lacking for 10 years but was made possible through our work and our unique software. Pendás et al [15] carried out an IQA electron correlation analysis of several systems, but they used CCSD(T) densities. Despite the differences between the classical contributions of MP2 and CCSD(T), very similar conclusions are reached when it comes to their exchange-correlation parts of the IQA partition

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Conclusion