Molecular orbital and density functional

The hetero-Diels-Alder reaction of aldehydes 12 with 2-azabutadienes 13 (Scheme 8.5) has been studied using high-level ab-initio multiconfigurational molecular orbital and density functionality calculation methods [28]. 

However, even the best experimental technique typically does not provide a detailed mechanistic picture of a chemical reaction. Computational quantum chemical methods such as the ab initio molecular orbital and density functional theory (DFT) " methods allow chemists to obtain a detailed picture of reaction potential energy surfaces and to elucidate important reaction-driving forces. Moreover, these methods can provide valuable kinetic and thermodynamic information (i.e., heats of formation, enthalpies, and free energies) for reactions and species for which reactivity and conditions make experiments difficult, thereby providing a powerful means to complement experimental data. 

Truong, T. N. and E. V. Stefanovich. 1995. A new method for incorporating solvent effects into classical, ab initio molecular-orbital and density functional theory frameworks for arbitrary shape cavity. Chem. Phys. Lett. 240, 253. 

The use of computational chemistry to address issues relative to process design was discussed in an article. The need for efficient software for massively parallel architectures was described. Methods to predict the electronic structure of molecules are described for the molecular orbital and density functional theory approaches. Two examples of electronic stracture calculations are given. The first shows that one can now make extremely accurate predictions of the thermochemistry of small molecules if one carefully considers all of the details such as zero-point energies, core-valence corrections, and relativistic corrections. The second example shows how more approximate computational methods, still based on high level electronic structure calculations, can be used to address a complex waste processing problem at a nuclear production facility (Dixon and Feller, 1999). 

The conformational properties of bridged biphenylenes, l,2,4,5-tetrahydrobiphenyleno[l,8-r/initio molecular orbital and density functional theory (DFT) methods. Studies on the Hartree-Fock (HF)/6-31G level of theory revealed that for 5, a plane symmetrical boat conformation was of the lowest energy. The twist, twist-boat, and chair conformations are less stable by 2.41, 5.02, and 2.62 kcal mol-1, respectively. Contrary, the twist conformation was found to be the most stable form for 4 <2003JMT(637)115>. 

Conformational energy maps for the furanosyl and pyranosyl rings of ribose and 2-deoxyribose in solution, generated with the MM3 force field, indicated the presence of several tautomers in multiple conformations for both compounds." The preferred conformations and energy pseudorotational barriers of 2-deoxy-P-D-ribofuranosylamine in protonated and unprotonated form have been established by use of ab initio molecular orbital and density functional theory calculations. Three-, two- and one-bond spin coupling constants in anhyd-... 

Jemmis, E.D. and Pancharatna, P.D. (2003) Condensed polyhedral boranes and analogous organometallic clusters a molecular orbital and density functional theory study on the cap-cap interactions. Appl. Organomet. Chem., 17 (6-7), 480 492. 

Ue, M., A. Murakami, and S. Nakamura. 2002. Anodic stability of several anions examined by ab initio molecular orbital and density functional theories. Journal of the Electrochemical Society 149 A1572-A1577. 

Ue, M. Murakami, A. Nakamura, S. Anodic Stability of Several Anions Examined by Ab Initio Molecular Orbital and Density Functional Theories, J. Electrochem. Soc. 2002, 149, A1572-A1577. 

Ab initio molecular orbital and density functional studies on the stable structures and vibrational properties of trans- and cis-azobenzenes ... 

Arulmozhiraja S, Fujii T, Tokiwa H. In+ cation interactions with some organics Ab initio molecular orbital and density functional theory. Chem Phys. 1999 250 237-42. 

In parallel with these advances in experimental techniques, the rapid and so far unending rise in computer power has led to the emergence of computational methods. The mathematical basis for quantum mechanics was laid out by Erwin Schrodinger and Paul Dirac in 1926, leading to their joint award of a Nobel Prize in 1933, but it was the prize awarded to John Pople and Walter Kohn in 1998 that at last recognized their roles in the development of the indispensable modern-day ab initio molecular orbital and density functional theories. 

A molecular-orbital and density-functional theory study has been reported for the mechanism of 2- -1-cycloaddition of hydrogen isocyanide to alkenes. The... 

Light has profound effect, both beneficial and harmful, on all of life. In this chapter, we consider a beneficial effect of visible light on repairing harmful changes induced by UV light in DNA. The harm is the dimerization of pyrimidines in DNA from UV radiation, the repair is the photoreactivation of the dimers by visible light. In particular we focus on the molecular level characterization of the photoreactivation process. Our discussion is based on the application of ab initio molecular orbital and density functional methods to this molecular process. 

The estimation of properties from molecular structures is the task of deriving specific chemical, physical, and thermodynamic properties, for a chemical compound or a mixture of chemical compounds, under a specific set of conditions (usually temperature, pressure, and phase), based primarily on information about the molecular structures of the compounds involved (and the composition, in the case of a mixture). While many modem techniques (including molecular modeling, ab initio or semiempirical quantum-chemical computations of molecular orbitals, and density functional theory) involve substantial computational effort for any one system (molecule or simple mixture) they study, other methods involve direct correlations between property values and particular features of the molecular structures involved. The latter methods involve regression of a model with experimental data over a class of compounds these methods favor empirical approximations and arguments over fundamental models. 

---