Computational chemistry density functional method

In particular, reactions involving transition-metals have attracted a lot of interest recently because of the connection to catalytic and enzymatic processes. Unfortunately, the proper computational description of such reactions is one of the great challenges of today s theoretical chemistry and the question for the general applicability of density functional methods in the field is an area of active research. We chose to provide a single but - as we think - representative example to illustrate the difficulties one has to face in theoretical studies of transition-metal reactivity. 

St-Amant, A. Density Functional Methods in Biomolecular Modeling, Reviews in Computational Chemistry 7, K. Lipkowitz and D. B. Boyd, eds. New York, VCH Publishers, 217-259. 

Ab-initio CAChe features all of the above plus ab-initio and density functional methods. This program requires a workstation (Windows NT minimum or SGI and IBM unix-based machines) and can be used to build and visualize results from ab-initio programs (e.g., Gaussian, see description under Gaussian, Inc.). Also, CAChe directly interfaces to Dgauss , a computational chemistry package that uses density functional theory to predict molecular structures, properties, and energetics. 

A. Nagy, in Recent Advances in Computational Chemistry, vol. 1 Recent Advances in the Density Functional Methods, Eds. V. Barone, A. Bencini, and P. Fantucci (World Scientific, Singapore, 2002), Part III, p. 247. 

St-Amant A. Density functional methods in biomolecular modeling. In Lipkowitz KB, Boyd DB, eds. Reviews in Computational Chemistry. Vol. 7. New York VCH, 1995 217-259. 

In recognition of the rapid expansion of computational chemistry in the 1980s, Andre Bandrauk and Andre Michel of the University of Sherbrooke organized the First Canadian Symposium on Computational Chemistry in May 1991 in Orford, Quebec. The conference included invited papers on dynamics, density functional methods, molecular modeling, Monte Carlo methods, and topics in quantum chemistry and statistical mechanics. About half of the invited speakers were from abroad (mostly from the United States). 

Abstract You can calculate molecular geometries, rates and equilibria, spectra, and other physical properties. The tools of computational chemistry are molecular mechanics, ab initio, semiempirical and density functional methods, and molecular dynamics. Computational chemistry is widely used in the pharmaceutical industry to explore the interactions of potential drugs with biomolecules, for example by docking a candidate drug into the active site of an enzyme. It is also used to investigate the properties of solids (e.g. plastics) in materials science. It does not replace experiment, which remains the final arbiter of truth about Nature. 

The quantum mechanical methods described in this book are all molecular orbital (MO) methods, or oriented toward the molecular orbital approach ab initio and semiempirical methods use the MO method, and density functional methods are oriented toward the MO approach. There is another approach to applying the Schrodinger equation to chemistry, namely the valence bond method. Basically the MO method allows atomic orbitals to interact to create the molecular orbitals of a molecule, and does not focus on individual bonds as shown in conventional structural formulas. The VB method, on the other hand, takes the molecule, mathematically, as a sum (linear combination) of structures each of which corresponds to a structural formula with a certain pairing of electrons [16]. The MO method explains in a relatively simple way phenomena that can be understood only with difficulty using the VB method, like the triplet nature of dioxygen or the fact that benzene is aromatic but cyclobutadiene is not [17]. With the application of computers to quantum chemistry the MO method almost eclipsed the VB approach, but the latter has in recent years made a limited comeback [18],... 

These developments have in turn renewed the interest in understanding the structure and reactivity of radical cations. Modern computational chemistry methods, especially density functional methods, as well as the continued exponential increase in hardware performance provided improved tools for a detailed analysis of these interesting species. At the same time, the unique problems of the computational treatment of radical cations as well as the direct and indirect observation of these short-lived species continue to pose new challenges for the development of new theoretical and experimental methods. 

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