Models in chemistry

Theoretical chemistry works on models. My point of view on models in chemistry - and quantum chemistry in partieidar - has been expressed elsewhere [6] this view closely corresponds to that expressed by other eolleagues [7-11]. 1 suggested a partition of a quantum chemical model into three eomponents, and in my scientific practice I have always taken into consideration the presenee and interplay of these three components. The consideration of the evolution of the whole quantum ehemistiy suggests me now the introduction of a fourth component of the models. My revised partition of quantum chemical models may be put in the following form... 

Gorden, G., Gauw, R., Emmert, G. Bubnis, B. (1998) The kinetics and mechanism of 003-formation following the electrolysis of salt brine what role do CIO2 and/or O3 play . Models in Chemistry, 135(5), 799-809. 

R. S. Drago. Applications of Electrostatic-Covalent Models in Chemistry. Surfside Gainesville, 1994. 

Consider a molecular structure, which is the most important unifying information model in chemistry. Molecular structures appear in knowledgebases that represent catalogs of commercially available chemicals, pharmacology of named drugs, natural sources of bioactive molecules, protein-ligand interactions, measured molecular bioactivities, metabolic pathways, abstracted research literature, databases of synthetic reactions, and so on. 

Seiler and Dunitz point out that the main reason for the widespread acceptance of the simple ionic model in chemistry and solid-state physics is its ease of application and its remarkable success in calculating cohesive energies of many types of crystals (see chapter 9). They conclude that the fact that it is easier to calculate many properties of solids with integral charges than with atomic charge distributions makes the ionic model more convenient, but it does not necessarily make it correct. 

In the 2-level limit a perturbative approach has been used in two famous problems the Marcus model in chemistry and the small polaron model in physics. Both models describe hopping of an electron that drags the polarization cloud that it is formed because of its electrostatic coupling to the enviromnent. This enviromnent is the solvent in the Marcus model and the crystal vibrations (phonons) in the small polaron problem. The details of the coupling and of the polarization are different in these problems, but the Hamiltonian formulation is very similar. ... 

It is reasonable to expect that models in chemistry should be capable of giving thermodynamic quantities to chemical accuracy. In this text, the phrase thermodynamic quantities means enthalpy changes AH, internal energy changes A U, heat capacities C, and so on, for gas-phase reactions. Where necessary, the gases are assumed ideal. The calculation of equilibrium constants and transport properties is also of great interest, but I don t have the space to deal with them in this text. Also, the term chemical accuracy means that we should be able to calculate the usual thermodynamic quantities to the same accuracy that an experimentalist would measure them ( 10kJmol-1). 

The isoinversion principle. A general selection model in chemistry, Angew. Chem. 1991, 103, 480-518 Angew. Chem,... 

Kozma, R. B., J. Russell, T. Jones, E. Katman, N. Marx, N. Davis, and J. Wykoff (1993) Interactive multimedia and mental models in chemistry A final report to the National Science Foundation, DUE-9150617. 

Paul G. Mezey, Mathematical Modeling in Chemistry. Based on a symposium held in Honolulu, Hawaii, December 17-22, 1989, VCH, Weinheim, 1991. 

Domenicano, A. Hargittai, I. Acta Chim. Hung.—Models in Chemistry 1993,130, 347. 

Hargittai, I. K lmdn, A. (Guest Eds.). A. 1. Kitaigorodskii Memorial Issue on Molecular Crystal Chemistry. Acta Chim. Hung.—Models in Chemistry 1993, Vol. 130, Nos. 2 and 3. 

Nakatsuji H (1992) Acta Chim Hungarica, Models in Chemistry 129 719. 

P. M. Zorky, The Development of Organic Crystal Chemistry at the Moscow State University. ACH—Models in Chemistry 1993, 130, 173-181. 

See, e.g., K. Mirsky, Early Days in the Atom—Atom Potential Approach to Intermolecular Interactions. ACH—Models in Chemistry 1993, 130,... 

A. Gavezzotti and G. Filippini, The Crystal Packing of Chlorine-and Sulfur-Containing Compounds." A( H Models in Chemistry 1993, 130, 205-220, and references therein. 

Mirsky, ACH—Models in Chemistry, 197—204 Gavezzotti, Filippini, ACH— Models in Chemistry, 205—220. 

Some models may appear very different from the objects they represent-Such "abstract" models may be rewarding because they are likely to reveal qualities of a system that may not even be suspected- There are numerous worthy models and modeling in chemistry relating to structures, reactions, transition states, spectra, bulk or local properties of large molecules, etc- Fig- 1 shows how a standard organic chemistry text [l] "models" the molecule of benz[a]anthracene and various other modelings of this benzenoid system at various levels of abstaction-... 

In developing madiematical modeling in chemistry and physics various branches of mathematics have been widely employed, frequently each with a well defined domain of applicability This sometimes has not been sufficiently emphasized or recognized, particularly when less familiar or less frequently used mathematical disciplines are involved, such as combinatorics, topology, graph theory, set theory or category theory The lack of appreciation of the specifics of each such discipline... 

However, although laws summarize observed behavior, they do nor tell us why nature behaves in the observed fashion. This is the central question for scientists. To try to answer this question, we construct theories (build models). The models in chemistry consist of speculations about what the individual atoms or molecules (microscopic particles) might be doing to cause the observed behavior of the macroscopic systems (collections of very large numbers of atoms and molecules). 

I. Gutman, E.V. Konstantinova, V.A. Skorobogatov, Molecular Hypergraphs and Clar Structural Formulas of Benzenoid Hydrocarbons, Acta Chimia Hungaria - Models in Chemistry, 5-6 (1999) 539-548. 

The most striking advance in solid state modelling in chemistry in the last decade is the rapid increase in the use of plane wave methods, mostly because there are several readily-available programs and graphical interfaces have made them more user-friendly. I shall discuss both the basis and developments of these methods and of the alternative localised function approach, but first I shall mention some concepts that are common to both approaches. 

W. Ehm, H. Gohr, R. Kaus, B. Roseler, and C. A. Schiller, "The Evaluation of Electrochemical Impedance Spectra Using a Modified Logarithmic Hilbert Transform," ACH-Models In Chemistry, 137 (2000) 145-157. 

Models play a major role in science. A model represents an object, a system, a process, or an idea. A model is also simpler than the actual thing that is modeled. In chemistry, models can be most useful in understanding what is happening at the microscopic level. In this book, you will see numerous illustrations showing models of chemical substances. These models, such as the ones shown in Figure 14, are intended to help you understand what happens during physical and chemical changes. 

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