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Details Collect From Order a copy Copyright or permission restrictions may apply. We will contact you if necessary. To learn more about Copies Direct watch this short online video. Need help? How do I find a book? Can I borrow this item? This chapter discusses contemporary quantum chemical methods and provides general insights into modern electronic structure theory with a focus on heavy-element-containing compounds.
We first give a short overview of relativistic Hamiltonians that are frequently applied to account for relativistic effects. Then, we scrutinize various quantum chemistry methods that approximate the N -electron wave function. In this respect, we will review the most popular single- and multi-reference approaches that have been developed to model the multi-reference nature of heavy element compounds and their ground- and excited-state electronic structures.
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Specifically, we introduce various flavors of post-Hartree—Fock methods and optimization schemes like the complete active space self-consistent field method, the configuration interaction approach, the Fock-space coupled cluster model, the pair-coupled cluster doubles ansatz, also known as the antisymmetric product of 1 reference orbital geminal, and the density matrix renormalization group algorithm. Furthermore, we will illustrate how concepts of quantum information theory provide us with a qualitative understanding of complex electronic structures using the picture of interacting orbitals.
While modern quantum chemistry facilitates a quantitative description of atoms and molecules as well as their properties, concepts of quantum information theory offer new strategies for a qualitative interpretation that can shed new light onto the chemistry of complex molecular compounds. Knowledge of the electronic structure of transition-metal complexes is increasingly being obtained through joint efforts by theory and experiments.
Here, we describe a variety of examples where spectroscopy is being used to determine, e. Both enzymatic and biomimetic systems are included, from the literature and from our own laboratories. It is shown that the combined efforts of wet and dry laboratories lead to a more profound understanding, and allows for systematic exploration of coordinate chemistry around the central metal atom.
Close correlation between theoretical modeling and experimental spectroscopy allows for identification of the electronic and geometric structure of a system through its spectral fingerprint. This is can be used to verify mechanistic proposals and is a valuable complement to calculations of reaction mechanisms using the total energy as the main criterion.
For transition metal systems, X-ray spectroscopy offers a unique probe because the core-excitation energies are element specific, which makes it possible to focus on the catalytic metal. The core hole is atom-centered and sensitive to the local changes in the electronic structure, making it useful for redox active catalysts. The possibility to do time-resolved experiments also allows for rapid detection of metastable intermediates. Reliable fingerprinting requires a theoretical model that is accurate enough to distinguish between different species and multiconfigurational wavefunction approaches have recently been extended to model a number of X-ray processes of transition metal complexes.
Compared to ground-state calculations, modeling of X-ray spectra is complicated by the presence of the core hole, which typically leads to multiple open shells and large effects of spin—orbit coupling. This chapter describes how these effects can be accounted for with a multiconfigurational approach and outline the basic principles and performance.
It is also shown how a detailed analysis of experimental spectra can be used to extract additional information about the electronic structure. This chapter focuses on the current understanding of absorption properties of cobalamins from both spectroscopic and computational points of views. In addition, we will discuss some other unique derivatives including antivitamins, non-alkyl cobalamins, as well as reduced and super-reduced forms. Proper DFT functional choice is paramount in predicting electronic transitions and simulating the full spectrum reliably.
A detailed molecular-level understanding of the excited-state ES decay dynamics of transition metal complexes TMCs is vital to develop the next generation of light-active components in a wide variety of applications related to photochemistry, including optoelectronics, photocatalysis, dye-sensitized solar cells, artificial photosynthesis, photonics sensors and switches, and bioimaging.
Molecular Electronic Structures of Transition | Products | Metal, Electronics, Chemistry
After photoexcitation, TMCs can undergo a plethora of interconnected relaxation processes, which compete to each other and are controlled by the subtle interplay of electronic and geometrical rearrangements that take place during the ES deactivation dynamics at different timescales. Intrinsic factors such as i the spin and character of the electronically ES involved in the process and ii the energetic alignment and effective couplings between these states do play a protagonist role in determining the preferred deactivation channels.
Extrinsic factors, such as temperature, pressure, excitation wavelength, and environmental effects, can often strongly modify the outcome of the photochemical processes. As kinetic control is always at play, only the fastest processes among all possible deactivation channels are generally observed. Computational chemistry is a powerful and unique tool to provide a microscopic and time-resolved description of these complex processes, and it often constitutes the fundamental ingredient for the interpretation of time-resolved absorption and emission spectroscopic measurements.
This chapter provides first a general overview on this complex topic, followed by an overview of the state-of-the-art quantum chemical and reaction dynamics methods to study the photodeactivation dynamics of TMCs and finally illustrates the progress and challenges in this field with recent examples from the literature. Importantly, these examples cover the ultrafast ES decay regime but also the long-lived photodeactivation from thermally equilibrated ES.
The use of computational methods based on electronic structure theory and statistical mechanics to study reaction mechanisms and kinetics in homogeneous catalysis, especially organometallic catalysis and organocatalysis , is reviewed.
Molecular electronic structures of transition metal complexes /
It is argued that while it plays a valuable role in mechanistic studies, computation is not yet able to replace experimental studies. Chromium, molybdenum and tungsten oxides supported on amorphous silica are catalysts for many reactions, including large-scale industrial processes. Although these systems have been extensively studied for many years, there are still a few unresolved issues, concerning mainly the nature of the active sites and mechanisms of their formation. Computational studies, using cluster or periodic models to represent the catalyst surface, are helpful in interpretation of spectroscopic data and can provide complementary information about the catalytic process.
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It is seen that coordination environment of the transition metal, determined also by local surface properties, is a key factor influencing catalytic activity of the surface metal species. This results in complex structure—activity relationships. While a great progress has been achieved in modelling of these systems, from simple clusters to advanced periodic slabs, theoretical determination of complex reaction mechanisms using surface models with representative distribution of metal sites is still a challenge for computational catalysis.
This chapter is the review of the computational methods applied to the transition metal oxides most abundant in heterogeneous catalysis and is focused on the influence of the environment on the transition metal cation properties. The shortcomings of the most commonly used DFT level of theory are discussed, and its extensions towards more realistic environment are presented.
The modern reactive force-field methods are also mentioned. The embedding schemes most commonly found in the quantum-chemical or classical description of the heterogeneous processes are discussed. The errors stemming from the non-completeness of the basis function, i. It is shown that in all discussed systems, i. This contribution shows how molecular electrochemistry may benefit from the application of DFT methods combined with implicit solvent models.
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