We are left with the inescapable conclusion that this scheme can serve as neither explanandum nor explanans i. There is no advantage in creating an infinitely flexible hybridization scheme. In the twenty-first century, every textbook of organic chemistry that we have examined introduces at least one hybridization model, with neither critical assessment nor explanation, to provide information about the orientation of chemical bonds in molecules of organic compounds.
Another common lore in chemistry is that HAO must be taught, generally at the beginning, in every introductory course of organic chemistry. In , the American Chemical Society ACS provided a list of anchoring concepts to outline a map of the content for organic chemistry in an undergraduate curriculum. Hybrid orbitals are necessary [ emphasis added ] to describe the geometry of substituents on individual atoms e. A cursory examination of these three main points invokes further queries.
How are they better representations and for what reasons are they necessary? What is the relation of HAO to the molecular-orbital or valence-bond theories of bonding? With the related term hybridization, HAO have been used traditionally to describe, to explain and to predict concepts in organic chemistry. Since its inception, the original concept of hybridization has been used for explanation.
Hybridization provides a simple explanation for the molecular shapes and bond angles of organic molecules; i. The position and shape of purported non-bonding valence electrons, known as lone pairs, in hybrid atomic orbitals have been invoked to explain reactivity. The existence of rabbit-ear hybrids on oxygen has been attacked, 29 , 30 defended, 31 and attacked again. We have demonstrated in Part 1 that an attempt to use hybrids as pseudo-explanation is never warranted.
Furthermore, hybrid orbitals have been invoked for their predictive power -- a tool so basic to predict trends that it requires no further description or justification. Some examples follow. Hybridization of orbitals has been related to the electronegativity of the central atom. The more s character that a hybrid orbital has, the nearer the nucleus that the electrons associated with that hybrid tend to exist.
A sp 2 hybrid on C can thus be deduced to have a relative electron-attractive power of C greater than that of H, whereas a carbon atom utilizing an sp 3 hybrid is predicted to have electronegativity similar to that of a hydrogen atom. The strength of a C-H bond is roughly predictable using hybridization.
This prediction has obvious utility in an interpretation of the force parameters used to assign absorption lines in an infrared spectrum of an organic compound.
The acidity of a proton might be envisaged to be influenced by some hybridization effect. Alkynes C-H utilizing sp hybridization are more acidic than alkenes C-H with sp 2 hybridization. One might be able to predict the order of acidity using the effect of hybridization. We contend that the use of HAO should be debated not on the prospective utility of the model, but rather on the mathematical constructs used to create the model.
These objections apply equally to dsp 2 or d 2 sp 3 or any other hybrid function that involves more than one p or d component. First, there is no need for hybridization as a consequence of quantum mechanics. As Lewars clearly showed, the formation of HAO is never necessary, and, whether or not one invokes sp 3 hybridization for calculations on methane, one obtains the same tetrahedral structure. Nor is hybridization a consequence of quantum laws. Second, the hybrid concept implies only the wave function of the atomic electrons.
Notwithstanding the confusion between geometry and hybridization, describing a an atomic center in a molecule or b a lone pair or c a bond as a hybrid is completely unacceptable. Many organic molecules contain unequal bond angles around the central atom e. A search of Internet scholar.
Hybrids are atomic orbitals and, by definition, are perturbed during the formation of a molecule; one cannot thus apply a hybridization label for lone pairs and bonds in molecules. Third, one cannot claim hybridization as the cause of an observation. Hybridization is not an actual physical phenomenon. Fourth, no direct experimental evidence for HAO exists. Fifth, HAO constitute a flawed model, limited by simple trigonometry, that nevertheless continues to influence the contemporary teaching of structural organic chemistry. A simple model of sp 3 , sp 2 , sp hybrids describes no real molecule.
One might compare this model to wooden or plastic models of molecules, which are also simple models but which are not designed to reproduce the complicated reality of molecular structure, even though they illustrate some salient features. Whereas we have found no claimant that insists that wooden models are mathematically and experimentally correct, the same cannot be said of the HAO model. Why should one continue with this, or other, flawed model? As HAO have, however, a mathematical basis, their precision or imprecision is based on mathematics.
A flawed model based on flawed mathematics must be unacceptable. Sixth, the method of applying sp 3 , sp 2 and sp HAO is not generally applicable to all organic molecules. Simple examples of hybridization are not extensible convincingly to more complicated organic structures, even with small alterations of structure. This theory is used to explain the covalent bond formation in many molecules.
Since the nature of the overlapping orbitals are different in H 2 and F 2 molecules, the bond strength and bond lengths differ between H 2 and F 2 molecules. In an HF molecule the covalent bond is formed by the overlap of the 1 s orbital of H and the 2 p z orbital of F, each containing an unpaired electron. Mutual sharing of electrons between H and F results in a covalent bond in HF. From Wikipedia, the free encyclopedia. One of two foundational theories of quantum chemistry.
The Chemical Bond 2nd ed. Bibcode : Natur. Hiberty New Jersey: Wiley-Interscience.
Coulson—Fischer theory Generalized valence bond Modern valence bond. Concepts Hybrid orbital Resonance Lewis structure. Norbornane: An investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories. Knippenberg, S. We report on the results of an exhaustive study of the valence electronic structure of norbornane C7H12 , up to binding energies of 29 eV.
Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than Despite this complication, they enable insights within 0.
Extending density functional embedding theory for covalently bonded systems. Quantum embedding theory aims to provide an efficient solution to obtain accurate electronic energies for systems too large for full-scale, high-level quantum calculations. It adopts a hierarchical approach that divides the total system into a small embedded region and a larger environment, using different levels of theory to describe each part. Previously, we developed a density-based quantum embedding theory called density functional embedding theory DFET , which achieved considerable success in metals and semiconductors.
In this work, we extend DFET into a density-matrix-based nonlocal form, enabling DFET to study the stronger quantum couplings between covalently bonded subsystems. We name this theory density-matrix functional embedding theory DMFET , and we demonstrate its performance in several test examples that resemble various real applications in both chemistry and biochemistry. DMFET gives excellent results in all cases tested thus far, including predicting isomerization energies, proton transfer energies, and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps for local chromophores.
Here, we show that DMFET systematically improves the quality of the results compared with the widely used state-of-the-art methods, such as the simple capped cluster model or the widely used ONIOM method. Advanced General Education Program. Each of the lessons concludes with a Mastery Test to be completed by the student.
Can the second order multireference perturbation theory be considered a reliable tool to study mixed- valence compounds? In this paper, the problem of the calculation of the electronic structure of mixed- valence compounds is addressed in the frame of multireference perturbation theory MRPT.
Using a simple mixed- valence compound the 5,5 ' 4H,4H ' -spirobi[ciclopenta[c]pyrrole] 2,2 ' ,6,6 ' tetrahydro cation , and the n-electron valence state perturbation theory NEVPT2 and CASPT2 approaches, it is shown that the ground state GS energy curve presents an unphysical "well" for nuclear coordinates close to the symmetric case, where a maximum is expected.
This behavior is rationalized using a simple model the ionized GS of two weakly interacting identical systems, each neutral system being described by two electrons in two orbitals , showing that the unphysical well is due to the canonical orbital energies which at the symmetric delocalized conformation lead to a sudden modification of the denominators in the perturbation expansion. In this model, the bias introduced in the second order correction to the energy is almost entirely removed going to the third order.
With the results of the model in mind, one can predict that all MRPT methods in which the zero order Hamiltonian is based on canonical orbital energies are prone to present unreasonable energy profiles close to the symmetric situation. However, the model allows a strategy to be devised which can give a correct behavior even at the second order, by simply averaging the orbital energies of the two charge-localized electronic states.
Such a strategy is adopted in a NEVPT2 scheme obtaining a good agreement with the third order results based on the canonical orbital energies. The answer to the question reported in the title is this theoretical approach a reliable tool for a correct description of these systems? The quaternary phase Ca5Mg0. The experimental space group Pnma in the nonstandard setting Pmcn corresponds to a klassengleiche symmetry reduction of index two of the predicted space group Cmcm.
This transition originates from the switching of one Ge and one Ag position in the TiNiSi-related slab, a process that triggers an uncoupling of each of the five 8f sites in Cmcm into two 4c sites in Pnma. The compound is deficient by one valence electron according to the Zintl concept, but LMTO electronic structure calculations indicate electronic stabilization and overall bonding optimization in the polyanionic network. Other stability factors beyond the Zintl concept that may account for the electronic stabilization are discussed.
Halogen bonding from a hard and soft acids and bases perspective: investigation by using density functional theory reactivity indices. It is found that the relative importance of electrostatic and orbital charge transfer interactions varies as a function of both the donor and acceptor molecules. Hard and soft interactions were distinguished and characterised by atomic charges, electrophilicity and local softness indices. The characteristic signal found in the reduced density gradient versus electron-density diagram corresponds to the non-covalent interaction between contact atoms in the NCI plots, which is the manifestation of halogen bonding within the NCI theory.
The unexpected C-X bond strengthening observed in several cases was rationalised within the molecular orbital framework. The importance of the energy of resonance of single bonds and double bonds in stabilizing octahedral complexes of chromium and manganese with carbonyl, phosphine, arsine, and thio groups is also discussed. A Multidimensional Measure of Work Valences. Work valence is derived from expectancy- valence theory and the literature on children's vocational development and is presumed to be a general appraisal of work that emerges during the childhood period.
Work valence serves to promote and inhibit the motivation and tasks associated with vocational development. A measure of work valence , composed of…. Rotational symmetry breaking toward a string- valence bond solid phase in frustrated J1 -J2 transverse field Ising model. We show that harmonic quantum fluctuations based on single spin flips can not lift such degeneracy, however an-harmonic quantum fluctuations based on multi spin cluster flip excitations lift the degeneracy toward a unique ground state with string- valence bond solid VBS nature.
A cluster operator formalism has been implemented to incorporate an-harmonic quantum fluctuations. We show that cluster-type excitations of the model lead not only to lower the excitation energy compared with a single-spin flip but also to lift the extensive degeneracy in favor of a string-VBS state, which breaks lattice rotational symmetry with only two fold degeneracy.
The tendency toward the broken symmetry state is justified by numerical exact diagonalization. Moreover, we introduce a map to find the relation between the present model on the checkerboard and square lattices. A minimalistic approach to static and dynamic electron correlations: Amending generalized valence bond method with extended random phase approximation correlation correction. A perfect-pairing generalized valence bond GVB approximation is known to be one of the simplest approximations, which allows one to capture the essence of static correlation in molecular systems.
In spite of its attractive feature of being relatively computationally efficient, this approximation misses a large portion of dynamic correlation and does not offer sufficient accuracy to be generally useful for studying electronic structure of molecules. We propose to correct the GVB model and alleviate some of its deficiencies by amending it with the correlation energy correction derived from the recently formulated extended random phase approximation ERPA. Thanks to a balanced treatment of static and dynamic correlation, ERPA-GVB stays reliable when one moves from systems dominated by dynamic electron correlation to those for which the static correlation comes into play.
The theory of hybrid bond orbitals is used to calculate equations giving the value of the bond angle OC—M—CO in relation to the bond number of the metal—carbonyl bond for tricarbonyl groups in which the transition-metal atom is enneacovalent or octacovalent and the group has approximate trigonal symmetry.
This agreement provides strong support for the theory. Worry amplifies theory -of-mind reasoning for negatively valenced social stimuli in generalized anxiety disorder. Theory -of-mind ToM is the ability to accurately infer others' thoughts and feelings. In generalized anxiety disorder GAD , cognitive and emotion regulation theories allude to the plausibility that ToM is conditional on the degree of individuals' state worry, a hallmark symptom.
GAD and state worry may interact to predict ToM constructs. However, no experiments have directly tested such interactional hypotheses, and used ToM as a framework to advance understanding of social cognition in GAD. This study therefore aimed to address this gap. GAD status significantly interacted with state worry to predict accuracy of overall reasoning, cognitive-reasoning, positive-reasoning, and negative-reasoning ToM. Worry, as opposed to relaxation, led sufferers of GAD to display more accurate overall reasoning and cognitive-reasoning ToM than controls, especially for negative signals.
Participants with GAD who worried, but not relaxed, were also significantly better than the norm at interpreting negative signals. These findings remained after controlling for gender, executive function, social anxiety, and depressive symptoms. For other ToM abilities, mean scores of persons with and without GAD who either worried or relaxed were normative.
The ToM reasoning measure lacked self-reference, and these preliminary findings warrant replication. Theoretical implications, such as the state worry-contingent nature of ToM in GAD, and clinical implications are discussed. The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals TMs of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states CSW-DOSs , where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs.
In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials. The magnetic properties of the complexes were studied in detail both experimentally and theoretically.
Unified Valence Bond Theory of Electronic Structure Applications
All dinuclear complexes show ferromagnetic intramolecular interactions, which were justified on the basis of the electronic structures of the Mn II and Mn III ions. The large Mn II -O-Mn III bond angle and small distortion of the Mn II cation from the ideal square pyramidal geometry were shown to enhance the ferromagnetic interactions since these geometrical conditions seem to favor the orthogonal arrangement of the magnetic orbitals. Variational theory of valence fluctuations: Ground states and quasiparticle excitations of the Anderson lattice model.
A variational study of ground states of the orbitally nondegenerate Anderson lattice model, using a wave function with one variational parameter per Bloch state k, has been extended to deal with essentially metallic systems having a nonintegral number of electrons per site. This approach provides a simple and explicit realization of the Luttinger picture of a periodic Fermi liquid. The occupation-number distribution for the conduction orbitals displays a finite discontinuity at the Fermi surface.
If the d-f hybridization is nonzero throughout the Brillouin zone, the quasiparticle spectrum will always exhibit a gap, although this gap becomes exponentially small i. For the metallic case, with a nonintegral number of electrons per site, the Fermi level falls within one of the two sharp density peaks. The foregoing variational theory has also been refined by means of a trial wave function having two variational parameters per Bloch state k. The above qualitative features are all retained, with some quantitative differences, but there are also some qualitatively new features.
The most interesting of these is the appearance, within. Energy decomposition analysis of single bonds within Kohn-Sham density functional theory. An energy decomposition analysis EDA for single chemical bonds is presented within the framework of Kohn-Sham density functional theory based on spin projection equations that are exact within wave function theory. Chemical bond energies can then be understood in terms of stabilization caused by spin-coupling augmented by dispersion, polarization, and charge transfer in competition with destabilizing Pauli repulsions.
The EDA reveals distinguishing features of chemical bonds ranging across nonpolar, polar, ionic, and charge-shift bonds. The effect of electron correlation is assessed by comparison with Hartree-Fock results.
- A New Politics of Identity: Political Principles for an Interdependent World.
- Unified Valence Bond Theory of Electronic Structure Applications : N D Epiotis : ;
- Women Who Become Men: Albanian Sworn Virgins (Dress, Body, Culture Series)?
- Rural Transformation and Newfoundland and Labrador Diaspora: Grandparents, Grandparenting, Community and School Relations.
- Magnetic Resonance Imaging: Basis for Interpretation;
Substituent effects are illustrated by comparing the C-C bond in ethane against that in bis diamantane , and dispersion stabilization in the latter is quantified. Finally, three metal-metal bonds in experimentally characterized compounds are examined: a [Formula: see text]-[Formula: see text] dimer, the [Formula: see text]-[Formula: see text] bond in dizincocene, and the Mn-Mn bond in dimanganese decacarbonyl.
A test of Hirschi's social bonding theory : a comparison of male and female delinquency. In this study, Hirschi's social bonding theory is employed to identify what aspects of the theory can explain male and female delinquency and whether social bonding variables can equally explain male and female delinquency generalizability problem in a developing society, Turkey. The data include a two-stage-stratified cluster sample of 1, high school students from the central districts of Ankara, the capital of Turkey.
The findings suggest that social bonding variables play a more important role for male students than for female students. Furthermore, they indicate that components of the social bonding theory can equally explain both male and female delinquent acts. Interpretation of monoclinic hafnia valence electron energy-loss spectra by time-dependent density functional theory. We present the valence electron energy-loss spectrum and the dielectric function of monoclinic hafnia m -HfO2 obtained from time-dependent density-functional theory TDDFT predictions and compared to energy-filtered spectroscopic imaging measurements in a high-resolution transmission-electron microscope.
Fermi's golden rule density-functional theory DFT calculations can capture the qualitative features of the energy-loss spectrum, but we find that TDDFT, which accounts for local-field effects, provides nearly quantitative agreement with experiment. We furthermore elaborate on the first-principles techniques used, their accuracy, and remaining discrepancies among spectra. More specifically, we assess the influence of Hf semicore electrons 5 p and 4 f on the energy-loss spectrum, and find that the inclusion of transitions from the 4 f band damps the energy-loss intensity in the region above 13 eV.
We study the impact of many-body effects in a DFT framework using the adiabatic local-density approximation ALDA exchange-correlation kernel, as well as from a many-body perspective using "scissors operators" matched to an ab initio G W calculation to account for self-energy corrections. These results demonstrate some cancellation of errors between self-energy and excitonic effects, even for excitations from the Hf 4 f shell. We also simulate the dispersion with increasing momentum transfer for plasmon and collective excitation peaks.
Size-dependent disproportionation in nm regime and hybrid Bond Valence derived interatomic potentials for BaTaO2N. Interatomic potentials for complex materials like ceramic systems are important for realistic molecular dynamics MD simulations. Such simulations are relevant for understanding equilibrium, transport and dynamical properties of materials, especially in the nanoregime. Here we derive a hybrid interatomic potential based on bond valence BV derived Morse and Coulomb terms , for modeling a complex ceramic, barium tantalum oxynitride BaTaO2N.
This material has been chosen due to its relevance for capacitive and photoactive applications. However, the material presents processing challenges such as the emergence of non-stoichiometric phases during processing, demonstrating complex processing-property correlations. This makes MD investigations of this material both scientifically and technologically relevant. The BV based hybrid potential presented here has been used for simulating sintering of BaTaO2N nanoparticles nm under different conditions using the relevant canonical ensemble. Notably, we show that sintering of particles of diameter 10 nm in size results in the formation of a cluster of tantalum and oxygen atoms at the interface of the BaTaO2N particles.
This is in agreement with the experimental reports. The results presented here suggest that the potential proposed can be used to explore dynamical properties of BaTaO2N and related systems. This work will also open avenues for development of nanoscience-enabled aid-free sintering approaches to this and related materials.
Bonding reactivity descriptor from conceptual density functional theory and its applications to elucidate bonding formation. Condensed-to-atom Fukui functions which reflect the atomic reactivity like the tendency susceptible to either nucleophilic or electrophilic attack demonstrate the bonding trend of an atom in a molecule. Accordingly, Fukui functions based concepts, that is, bonding reactivity descriptors which reveal the bonding properties of molecules in the reaction were put forward and then applied to pericyclic and cluster reactions to confirm their effectiveness and reliability.
In terms of the results from the bonding descriptors, a covalent bond can readily be predicted between two atoms with large Fukui functions i. For SinOm clusters' reactions, the clusters with a low O atom ratio readily form a bond between two Si atoms with big values of their Fukui functions in which they respectively govern nucleophilic and electrophilic attacks or both govern radical attacks.
Also, our results from bonding descriptors show that Si—Si bonds can be formed via the radical mechanism between two Si atoms, and formations of Si—O and O—O bonds are possible when the O content is high. These results conform with experimental findings and can help experimentalists design appropriate clusters to synthesize Si nanowires with high yields. The approach established in this work could be generalized and applied to study reactivity properties for other systems. A corpuscular picture of electrons in chemical bond. We introduce a theory of chemical bond with a corpuscular picture of electrons.
Its accuracy for describing potential energy curves of chemical bonds in ground and excited states of spin singlet and triplet is examined. The small changes in electron-donating ability is modulated by the overlap with the coordinating metal ion's valence atomic orbitals. The finding of blue-shifts in certain complexes is of significant interest, which has led to numerous studies of the origins of the phenomenon.
Because charge transfer mixing i. Turning off the charge transfer mixing can be achieved by employing the block-localized wave function BLW method, which is an ab initio valence bond VB method. Further, with the BLW method, the overall stability gained in the formation of a complex can be analyzed in terms of a few physically meaningful terms. Thus, the BLW method provides a unified and physically lucid way to explore the nature of red- and blue-shifting phenomena in both hydrogen and halogen bonding complexes.
In this study, a direct correlation between the total stability and the variation of the Y-A bond length is established based on our BLW computations, and the consistent roles of all energy components are clarified. As a consequence, both the charge transfer and polarization stabilize bonding systems with the Y-A bond stretched and red-shift the vibrational frequency of the Y-A bond.
Notably, the energy of the frozen wave function is the only energy component which prefers the shrinking of the Y-A bond and thus is responsible for the associated blue-shifting.
- Valence bond theory.
- ISBN 13: 9783540120001?
- Advancing the Frontiers of (Bio)Chemistry with Valence Bond Approaches.
- Sacred Valley Adventures.
- Aspects of Positivity in Functional Analysis: Proceedings of the Conference Held on the Occasion of H.H. Schaefers 60th Birthday, Tubingen, 24-28 …!
- Intestinal Transport: Fundamental and Comparative Aspects.
- HYBRID ATOMIC ORBITALS IN ORGANIC CHEMISTRY. PART 2: CRITIQUE OF PRACTICAL ASPECTS.
- Book Unified Valence Bond Theory Of Electronic Structure.
The total variations of the Y-A bond length and the corresponding stretching vibrational frequency are thus. A test of Hirschi's social bonding theory : juvenile delinquency in the high schools of Ankara, Turkey.
Travis Hirschi's social bonding theory has mostly been tested in the West. In this study, the theory is tested on juvenile delinquency in a developing country, Turkey. Data were gathered from 1, high school students in Ankara by using two-stage stratified cluster sampling. Factor analysis was employed to determine the dimensions of juvenile delinquency assault, school delinquency, and public disturbance , and regression analysis was used to test the theory.
Similar to some other traditional societies, the social bonding theory plays an important role in the explanation of juvenile delinquency in Turkey. A second order thermodynamic perturbation theory for hydrogen bond cooperativity in water. It has been extensively demonstrated through first principles quantum mechanics calculations that water exhibits strong hydrogen bond cooperativity. Equations of state developed from statistical mechanics typically assume pairwise additivity, meaning they cannot account for these 3-body and higher cooperative effects.
In this paper, we extend a second order thermodynamic perturbation theory to correct for hydrogen bond cooperativity in 4 site water. We demonstrate that the theory predicts hydrogen bonding structure consistent spectroscopy, neutron diffraction, and molecular simulation data. Finally, we implement the approach into a general equation of state for water.
A density functional theory for colloids with two multiple bonding associating sites. Wertheim's multi-density formalism is extended for patchy colloidal fluids with two multiple bonding patches. The theory is developed as a density functional theory to predict the properties of an associating inhomogeneous fluid.
The equation of state developed for this fluid depends on the size of the patch, and includes formation of cyclic, branched and linear clusters of associated species.
The theory predicts the density profile and the fractions of colloids in different bonding states versus the distance from one wall as a function of bulk density and temperature. The predictions from our theory are compared with previous results for a confined fluid with four single bonding association sites. Also, comparison between the present theory and Monte Carlo simulation indicates a good agreement.
Maximum- valence radii of transition metals. In many of their compounds the transition metals have covalence 9, forming nine bonds with use of nine hybrid spd bond orbitals. A set of maximum- valence single- bond radii is formulated for use in these compounds. These radii are in reasonably good agreement with observed bond lengths. Quadruple bonds between two transition metal atoms are about 50 pm iron-group atoms or 55 pm palladium and platinum-group atoms shorter than single bonds. This amount of shortening corresponds to four bent single bonds with the best set of bond angles, Density functional theory study of the reaction mechanism for competitive carbon-hydrogen and carbon-halogen bond activations catalyzed by transition metal complexes.
Carbon-hydrogen and carbon-halogen bond activations between halobenzenes and metal centers were studied by density functional theory with the nonempirical meta-GGA Tao-Perdew-Staroverov-Scuseria functional and an all-electron correlation-consistent polarized valence double-zeta basis set. Our calculations demonstrate that the hydrogen on the metal center and halogen in halobenzene could exchange directly through a kite-shaped transition state.
Transition states with this structure were previously predicted to have high energy barriers J. These pathways include the ortho-C-H and Ti-H bond activations for the formation and release of H 2 and the indirect C-Cl bond activation via beta-halogen elimination for the movement of the C 6 H 4 ring and the formation of a C-N bond in the observed final product. Structure and capacitance of an electric double layer of an asymmetric valency dimer electrolyte: A comparison of the density functional theory with Monte Carlo simulations.
Here, the density functional theory is applied to a study of the structure and differential capacitance of a planar electric double layer formed by a valency asymmetric mixture of charged dimers and monomers. The dimer consists of two tangentially tethered hard spheres of equal diameters of which one is charged and the other is neutral, while the monomer is a charged hard sphere of the same size.
The dimer electrolyte is next to a uniformly charged, smooth planar electrode. Important consequences of asymmetry in charges and in ion shapes are i a finite, non-zero potential of zero charge, and ii asymmetric shaped and capacitance curves which are not mirror images of each other. Comparisons of the density functional results with the corresponding Monte Carlo simulations show the theoretical predictions to be in good agreement with the simulations overall except near zero surface charge. The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters.
The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. A density functional theory study on the hydrogen bonding interactions between luteolin and ethanol. Ethanol is one of the most commonly used solvents to extract flavonoids from propolis.
Hydrogen bonding interactions play an important role in the properties of liquid system. The main objective of the work is to study the hydrogen bonding interactions between flavonoid and ethanol. Luteolin is a very common flavonoid that has been found in different geographical and botanical propolis. In this work, it was selected as the representative flavonoid to do detailed research. The study was performed from a theoretical perspective using density functional theory DFT method.
In the optimized geometries, it is found that: 1 except for the H2', H5', and H6', CH 3 CH 2 OH has formed hydrogen bonds with all the hydrogen and oxygen atoms in luteolin. While the other hydrogen bonds are weak strength and possess a dominant character of the electrostatic interactions in nature. Reactive Force Fields via Explicit Valency. Computational simulations are invaluable in elucidating the dynamics of biological macromolecules.
Unfortunately, reactions present a fundamental challenge. Calculations based on quantum mechanics can predict bond formation and rupture; however they suffer from severe length- and time-limitations. At the other extreme, classical approaches provide orders of magnitude faster simulations; however they regard chemical bonds as immutable entities. A few exceptions exist, but these are not always trivial to adopt for routine use.
We bridge this gap by providing a novel, pseudo-classical approach, based on explicit valency. We unpack molecules into valence electron pairs and atomic cores. Particles bear ionic charges and interact via pairwise-only potentials. The potentials are informed of quantum effects in the short-range and obey dissociation limits in the long-range. They are trained against a small set of isolated species, including geometries and thermodynamics of small hydrides and of dimers formed by them.
The resulting force field captures the essentials of reactivity, polarizability and flexibility in a simple, seamless setting. Following the introduction in Chapter 1, we initially focus on the properties of water. Chapter 2 considers gas phase clusters. To transition to the liquid phase, Chapter 3 describes a novel pairwise long-range compensation that performs comparably to infinite lattice summations. The approach is suited to ionic solutions in general. In Chapters 4 and 5, LEWIS is shown to correctly predict the dipolar and quadrupolar response in bulk liquid, and can accommodate proton transfers in both acid and base.
Efficiency permits the study of proton defects at dilutions not accessible to experiment or quantum mechanics. Chapter 6 discusses explicit valency approaches in other hydrides, forming the basis of a reactive organic force field. Examples of simple. Bond breaking and bond formation: how electron correlation is captured in many-body perturbation theory and density-functional theory.
For the paradigmatic case of H 2 dissociation, we compare state-of-the-art many-body perturbation theory in the GW approximation and density-functional theory in the exact-exchange plus random-phase approximation RPA for the correlation energy. For an unbiased comparison and to prevent spurious starting point effects, both approaches are iterated to full self-consistency i.
The exchange-correlation diagrams in both approaches are topologically identical, but in sc-RPA they are evaluated with noninteracting and in sc-GW with interacting Green functions. We argue that for a given diagrammatic expansion, sc-RPA outperforms sc-GW when it comes to bond breaking. We attribute this to the difference in the correlation energy rather than the treatment of the kinetic energy. Ruthenium L3-edge X-ray absorption XA spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes.
The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory TDDFT is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy.
We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed- valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.
Cooperativity of halogen, chalcogen, and pnictogen bonds in infinite molecular chains by electronic structure theory. Halogen bonds XBs are intriguing noncovalent interactions that are frequently being exploited for crystal engineering. Recently, similar bonding mechanisms have been proposed for adjacent main-group elements, and noncovalent "chalcogen bonds " and "pnictogen bonds " have been identified in crystal structures. A fundamental question, largely unresolved thus far, is how XBs and related contacts interact with each other in crystals; similar to hydrogen bonding , one might expect "cooperativity" bonds amplifying each other , but evidence has been sparse.
Here, we explore the crucial step from gas-phase oligomers to truly infinite chains by means of quantum chemical computations. A periodic density functional theory DFT framework allows us to address polymeric chains of molecules avoiding the dreaded "cluster effects" as well as the arbitrariness of defining a "large enough" cluster. We focus on three types of molecular chains that we cut from crystal structures; furthermore, we explore reasonable substitutional variants in silico.
Two experimentally known organic crystals, albeit with similar atomic connectivity and XB characteristics, show signs of cooperativity in one case but not in another. We introduce the atomic valence active space AVAS , a simple and well-defined automated technique for constructing active orbital spaces for use in multiconfiguration and multireference MR electronic structure calculations.