Quantum chemical concepts

An analogous role has been played by other scientists in strengthening the ties between quantum chemistry of type I (and type II) with the area corresponding to biochemistry (or complex molecular systems in general), a task made more difficult by the explosive growth of structural and functional information about biomolecular systems. It is worth to remark here that such a fruitful use of quantum chemical concepts in biology has requested the extension of the methods to approaches different from quantum molecular theory in the strict sense introduced before. We shall comeA back to this remark later. 

Mathematics is now so central, so much inside , that without it we cannot hope to understand our chemistry. .. These (quantum-chemical) concepts have their origin in the bringing together of mathematics and chemistry. ... 

Visible Spectra of Conjugated Dyes Integrating Quantum Chemical Concepts with Experimental Data 174... 

Classical and recent quantum-chemical concepts about the electronic structure of M element compounds. The dependence of intramolecular electronic, steric and stereoelec -tronic interactions on the nature of the M atom and the M—Y bonds. 

The theoretical chemical application of surface chemical bonding theory, highlighted next, is related to formal chemisorption theory as developed in surface physics, but concentrates on quantum chemical concepts as the electron distribution over bonding and antibonding orbital fragments [5, 6]. It will be seen that both approaches complement each other. The notion of a surface molecule relates to the surface physicists concept of surface state. 

In this contribution, an approach to the quantum chemical concept of functional groups will be discussed, with special emphasis on their shapes, similarity and complementarity relations. 

Functional Groups and Their Shapes as Quantum Chemical Concepts A Density Domain Criterion for Functional Groups... 

The quantum chemical concept of local electron densities and the traditional organic chemistry concept of functional groups have much in common. 

Specific aspects of the quantum chemical concept of local electron densities and functional groups of chemistry have been discussed, with emphasis on the Additive Fuzzy Density Fragmentation (AFDF) Principle, on the Adjustable Density Matrix Assembler (ADMA) Method of using a local density matrix formalism of fuzzy electron density fragments in macromolecular quantum chemistry, and on the fundamental roles of the holographic electron density theorem, local symmetry, and symmetry deficiency. 

Quantum chemistry and quantum chemical concepts have had an enormous impact on chemistry, and this impact is accelerating. It is rare now to pick up a chemical journal and read an article in which quantum chemistry or concepts derived from quantum chemistry are not present. More and more experimental studies not only use concepts unknown a decade ago, but also... 

A new qualitative quantum-chemical concept of the elementary act of addition polymerization has been proposed as the development of the polymerization theory. An extensive set of various data on the kinetics and the mechanism of polymer structure controlling has been found to have a new explanation from an uniform viewpoint. This concept is developed in the framework of the axiomatic approach to the general polymerization theory and is based on five postulates, namely the principle of the intermediate, the principle of intermediate cyclicity, the principle of correspond-... 

A qualitative quantum-chemical concept of the elementary polymerization act is proposed as a development of the concepts of the polymerization mechanism on the basis of the available experimental data generalizes in the framework of quantum-mechanical concepts. Up to the present, this concept has been based on five postulates. 

Quantum chemistry has certainly come of age, and quantum chemical concepts appear in nearly all papers published in the chemical literature today. Actual quantum chemical calculations are now reported in many experimental papers, and computer codes that perform these calculations are now often considered as another piece of chemical apparatus. Various experimental groups now train experts in computational chemistry, along with experts in NMR spectroscopy, mass spectroscopy, and so on. Nearly all molecular electronic structure calculations today start with molecular orbital (MO) calculations, but the history of the development of this methodology is often forgotten. Today s heroes have become the writers of useful computer code, but the basic underpinnings of these codes, the ideas that let these codes develop and become useful and those who developed these ideas, are often forgotten. Who is Roothaan What did he do that so influenced MO theory I can make my distinction of theoretical chemist versus computational chemist, should such a distinction be appropriate, on the basis of this answer. This short manuscript reviews the 1951 paper by C.C.J. Roothaan entitled New developments in molecular orbital theory [1], hopefully putting this... 

In this section we introduce principles of the surface chemical bond. First principle ab initio computational results are analyzed using basic quantum-chemical concepts. In this section, we analyze the adsorption of molecules. In the following section, we analyze the adsorption of atoms. The adsorption of ammonia and CO is discussed first since they are known to interact predomenantly through donation and back-donation interactions, respectively. This will subsequently lead into the analysis of the stronger bonds that form between adatoms and a surface. We note the similarities in chemical bonding of these adsorbates to surfaces, clusters and organometallic complexes, and in addition describe some of the differences. 

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