Where Does Electron Correlation Lie? Some Answers from a Real Space Partition

Casalz-Sainz, José Luis; Guevara‐Vela, José Manuel; Francisco, E.; Rocha‐Rinza, Tomás; Pendás, Ángel Martín

doi:10.1002/cphc.201700940

Cited by 24 publications

(28 citation statements)

References 61 publications

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“…However, there is a physical explanation for this observation: while only employing the Hartree-Fock field, only Fermi correlation is considered (the Fermi hole [58] follows the electron and exclude same-spin electrons), which means that there is no correlation between electrons with opposite spin states. When Møller-Plesset perturbation is applied, Coulomb correlation becomes present in the system, and opposite-spin electrons are no longer independent [59]. This fact will cause repulsion between electrons, especially in covalent multiple bonds of low polarity.…”

Section: Discussionmentioning

confidence: 99%

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

2020

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The quantum topological energy partitioning method Interacting Quantum Atoms (IQA) has been applied for over a decade resulting in an enlightening analysis of a variety of systems. In the last three years we have enriched this analysis by incorporating into IQA the two-particle density matrix obtained from Møller-Plesset (MP) perturbation theory. This work led to a new computational and interpretational tool to generate atomistic electron correlation and thus topologically based dispersion energies. Such an analysis determines the effects of electron correlation within atoms and between atoms, which covers both bonded and non-bonded "throughspace" atom-atom interactions within a molecule or molecular complex. A series of papers published by us and other groups shows that the behavior of electron correlation is deeply ingrained in structural chemistry. Some concepts that were shown to be connected to bond correlation are bond order, multiplicity, aromaticity, and hydrogen bonding. Moreover, the concepts of covalency and ionicity were shown not to be mutually excluding but to both contribute to the stability of polar bonds. The correlation energy is considerably easier to predict by machine learning (kriging) than other IQA terms. Regarding the nature of the hydrogen bond, correlation energy presents itself in an almost contradicting way: there is much localized correlation energy in a hydrogen bond system, but its overall effect is null due to internal cancelation. Furthermore, the QTAIM delocalization index has a connection with correlation energy. We also explore the role of electron correlation in protobranching, which provides an explanation for the extra stabilization present in branched alkanes compared to their linear counterparts. We hope to show the importance of understanding the true nature of the correlation energy as the foundation of a modern representation of dispersion forces for ab initio, DFT, and force field calculations.

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Section: Discussionmentioning

confidence: 99%

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

2020

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“…It must be pointed out that there are some instances in which bond correlation can be negative, as we reported elsewhere [2] for some ionic bonds and most notably hydrides. In fact, Pendás et al [15] also reported the negative exchange-correlation components in the hydride BH 3 , justifying this observation by the poor Hartree-Fock description of the hydride-like atomic volume. The sign of the bond correlation energy is an indication of bond polarity: low polarity bonds have large positive bond correlation energies (the electronic density is concentrated at the interatomic region) because high polarity bonds have small or even negative bond correlations (the electronic density is concentrated at the atomic basins).…”

Section: Resultsmentioning

confidence: 96%

“…This capability was lacking for 10 years but was finally made possible through our work and our unique software. Furthermore, Pendás et al [15] also carried out an IQA electron correlation analysis of several systems, but they used CCSD(T) densities. In the paper, a quick comparison between MP2 and CCSD(T) densities shows that the use of the unrelaxed MP2 densities can result in incomplete descriptions of the kinetic and electrostatic terms in the IQA partition, especially when compared to the relaxed CCSD(T) densities.…”

Section: Introductionmentioning

confidence: 99%

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

Silva

Popelier

2018

J Mol Model

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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.

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“…Each of the six H–H pairs has an exchange‐correlation driven ISBE of about 5 kcal mol −1 . We have argued that these nonbonded terms are the short‐range remnants of long‐range dispersion . If we do not recognize these 1,3 secondary interactions and insist on assigning this stabilization to the chemical C−H bonds, then each C−H bond energy would acquire an extra (6×4.8)/4=7.2 kcal mol −1 stabilization energy.…”

Section: Theory and Discussionmentioning

confidence: 99%

Real‐Space In Situ Bond Energies: Toward A Consistent Energetic Definition of Bond Strength

Menéndez-Crespo

Costales

Francisco

et al. 2018

Chemistry A European J

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A rigorous definition of intrinsic bond strength based on the partitioning of a molecule into real-space fragments is presented. Using the domains provided by the quantum theory of atoms-in-molecules (QTAIM) together with the interacting quantum atoms (IQA) energetic decomposition, we show how an in situ bond strength, matching all the requirements of an intrinsic bond energy, can be defined between each pair of fragments. Total atomization or fragmentation energies are shown to be equal to the sum of these in situ bond energies (ISBEs) if the energies of the fragments are measured with respect to their in-the-molecule state. These energies usually lie above the ground state of the isolated fragments by quantities identified with the standard fragment relaxation or deformation energies, which are also provided by the protocol. Deformation energies bridge dissociation energies with ISBEs, and can be dissected by using well-known tools of real-space theories of chemical bonding. Similarly, ISBEs can be partitioned into ionic and covalent contributions, and this feature adds to the chemical appeal of the procedure. All the energetic quantities examined are observable and amenable, in principle, to experimental determination. Several systems, exemplifying the role of each energetic term presented herein, are used to show the power of the approach.

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Where Does Electron Correlation Lie? Some Answers from a Real Space Partition

Cited by 24 publications

References 61 publications

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

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

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

Real‐Space In Situ Bond Energies: Toward A Consistent Energetic Definition of Bond Strength

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