Covalent Bonding in the Hydrogen Molecule

Bacskay, George B.; Nordholm, Sture

doi:10.1021/acs.jpca.7b08963

Cited by 18 publications

(28 citation statements)

References 95 publications

(368 reference statements)

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“…Clearly, modern quantum theory can explain chemistry in all circumstances well, despite the continuous debate on the nature of 'chemical bond', including that present in the simplest of all molecules, H 2 . 85 The devil, indeed, is in the detail. We submit that all the atoms considered in this work are chemical, and all these homonuclear diatomic molecules are held together by 'chemical bonds'.…”

Section: Geometric Parametersmentioning

confidence: 97%

Chemical bonding in Period 2 homonuclear diatomic molecules: a comprehensive relook

Das

Arunan

2019

J Chem Sci

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Theoretical and experimental studies of bonding in the main group homonuclear diatomic molecules have been pursued for many years, and they possess serious challenges for scientists. Most of the early experimental work have been carried out by Herzberg. 1,2 We take a relook at the bonding motifs of Period 2 homonuclear diatomic molecules (from Li 2 to Ne 2) using varieties of quantum chemical tools, commonly used for intermolecular bonding/interactions now. The methods employed include Atoms in Molecules (AIM), Non-covalent Index plot (NCI), Electrostatic potential (ESP), and Potential Acting on one Electron in a Molecule (PAEM). The spectroscopic constants i.e., equilibrium bond distances (r e), harmonic frequencies (x), bond dissociation energies (D e) have all been evaluated using high-level ab initio methods and critically compared with the experimental results. Multi-reference calculations (CASSCF) on B 2 and C 2 have been carried out as they have a large number of low lying electronic states. Bonding within these homonuclear diatomic molecules show all the diversities that are encountered in inter/intra-molecular bonding in chemistry. Based on the AIM analysis, these 8 homonuclear diatomic molecules could be divided into three different groups, based on the correlation between binding energy and the electron density at the bond critical point. However, PAEM/ESP analysis allows us to analyse all eight of them as one group having a good correlation between binding energy and the PAEM/ESP at the critical point between the two atoms. Our results highlight the arbitrariness in relying on some computational tools to characterize a bond as covalent (shared) or ionic/electrostatic (closed). In contrast, they also show the usefulness of the various methods in exploring similarities and differences in bonding. We propose that from Li 2 to Ne 2 , all homonuclear diatomic molecules are bound by 'chemical bonds'.

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Section: Geometric Parametersmentioning

confidence: 97%

Chemical bonding in Period 2 homonuclear diatomic molecules: a comprehensive relook

Das

Arunan

2019

J Chem Sci

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“…The optimized orbital exponents ζ for H 2 + and H 2 vary between the separated H atoms limit of 1.0 (R = ∞), and the united He + and He atom limits of 2.0 and 1.688, respectively (R = 0), in atomic units (see Appendix A). While these simplest of wave functions can be improved upon so that their predictions become quantitative, e.g., by the inclusion of polarization functions and in the case of H 2 account for a greater degree of electron correlation, it has been found, more than once, that the basic physics of covalent bonding are adequately resolved by the above minimal sets [56,57,81,82]. Keeping the calculations as straightforward and simple as possible means that the essential elements of bonding can be clearly resolved with as little mathematical complexity as possible.…”

Section: Energy Analysis Of One-and Two-electron Bonds: the H 2 + Andmentioning

confidence: 99%

“…Unfortunately, his clear sighted reasoning, if after a change of heart, seems to have largely by-passed the attention of the chemical community. While our own work over a period of 25 years [68,69,72,75,[77][78][79][80][81][82][83], has agreed with Hellmann's [40], Ruedenberg's [49][50][51][52][53][54][55][56][57][58][59], and Feynman's [88] views, it has also expanded on them by exploring the quantum dynamical description of covalent bonding. Noting that Thomas-Fermi (TF) theory [41,42], the original and simplest type of density functional theory (DFT) [45,89], is unable to describe covalent bonding [43][44][45], we analyzed the reasons for this failure in an effort to better understand the basic physics of bonding [68,[78][79][80].…”

Section: Introductionmentioning

confidence: 99%

“…Instead it provides a fully consistent alternative interpretation which sheds light on covalent bonding while avoiding, or in a deeper analysis helping to resolve, the apparent contradiction between the theory and the theorem. The next section of this paper will review the salient features of Ruedenberg's [49][50][51][52][53][54][55][56][57][58][59] theory and our contributions to it [68,69,72,75,[77][78][79][80][81][82][83]. We regard it as most useful for those who want to understand covalent bonding in terms of time-independent interpretations of concepts such as electron density, delocalization and energy.…”

Section: Introductionmentioning

confidence: 99%

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The Basics of Covalent Bonding in Terms of Energy and Dynamics

Nordholm

Bacskay

2020

Molecules

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We address the paradoxical fact that the concept of a covalent bond, a cornerstone of chemistry which is well resolved computationally by the methods of quantum chemistry, is still the subject of debate, disagreement, and ignorance with respect to its physical origin. Our aim here is to unify two seemingly different explanations: one in terms of energy, the other dynamics. We summarize the mechanistic bonding models and the debate over the last 100 years, with specific applications to the simplest molecules: H2+ and H2. In particular, we focus on the bonding analysis of Hellmann (1933) that was brought into modern form by Ruedenberg (from 1962 on). We and many others have helped verify the validity of the Hellmann–Ruedenberg proposal that a decrease in kinetic energy associated with interatomic delocalization of electron motion is the key to covalent bonding but contrary views, confusion or lack of understanding still abound. In order to resolve this impasse we show that quantum mechanics affords us a complementary dynamical perspective on the bonding mechanism, which agrees with that of Hellmann and Ruedenberg, while providing a direct and unifying view of atomic reactivity, molecule formation and the basic role of the kinetic energy, as well as the important but secondary role of electrostatics, in covalent bonding.

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“…Ruedenberg, Bacskay, and Nordholm described the shape of the HKED in the bonding region of H þ 2 [64] whereas Preston and Bader examined the relationship between the topographical features of charge distribution and the kinetic energy of hydrogen molecule. [26] Figure 3 shows the profiles of K(r), G(r), r 2 G(r) and r 2 K(r) along the internuclear axis of the equilibrium geometry of the H 2 .…”

Section: Hydrogen Moleculementioning

confidence: 99%

Laplacian of the Hamiltonian Kinetic Energy Density as an Indicator of Binding and Weak Interactions

et al. 2019

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The kinetic energy is the center of a controversy between two opposite points of view about its role in the formation of a chemical bond. One school states that a lowering of the kinetic energy associated with electron delocalization is the key stabilization mechanism of covalent bonding. In contrast, the opposite school holds that a chemical bond is formed by a decrease in the potential energy due to a concentration of electron density within the binding region. In this work, a topographic analysis of the Hamiltonian Kinetic Energy Density (KED) and its laplacian is presented to gain more insight into the role of the kinetic energy within chemical interactions. This study is focused on atoms, diatomic and organic molecules, along with their dimers. In addition, it is shown that the laplacian of the Hamiltonian KED exhibits a shell structure in atoms and that their outermost shell merge when a molecule is formed. A covalent bond is characterized by a concentration of kinetic energy, potential energy and electron densities along the internuclear axis, whereas a charge-shift bond is characterized by a fusion of external concentration shells and a depletion in the bonding region. In the case of weak intermolecular interactions, the external shell of the molecules merge into each other resulting in an intermolecular surface comparable to that obtained by the Non-covalent interaction (NCI) analysis.

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Covalent Bonding in the Hydrogen Molecule

Cited by 18 publications

References 95 publications

Chemical bonding in Period 2 homonuclear diatomic molecules: a comprehensive relook

Chemical bonding in Period 2 homonuclear diatomic molecules: a comprehensive relook

The Basics of Covalent Bonding in Terms of Energy and Dynamics

Laplacian of the Hamiltonian Kinetic Energy Density as an Indicator of Binding and Weak Interactions

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