Density functional-based

To date the majority of QM-MM applications have employed density functional methods ab initio or semiempirical methods in the quantum region. The energy tenns evaluated in these methods are generally similar, but there are specific differences. The relevant equations for the density functional based methods are described first, and this is followed by a description of the specific differences associated with the other methods. 

For density functional based QM-MM methods the electronic energy terms depend explicitly on the electron density, p(r), of the atoms in the quantum region [46]. The... 

Koskinen, P., Hakkinen, H., Seifert, G Sanna, S., Frauenheim, Th. and Moseler, M. (2006) Density-functional based tight-binding study of small gold clusters. New Journal of Physics, 8, 9—11. 

Advances in Density-functional-based Modeling Techniques... 

Porezag, D. and Pederson, M. R Density functional based studies of transition states and barriers for hydrogen exchange and abstraction reactions, J. Chem.Phys., 102 (1993, 9345-9349... 

Wu and Cinar (1996) use a polynomial approximation (ARMENSI) of the error density function / based on a generalized exponential family, such as... 

The role of quantum theory in chemistry has a history of almost 100 years, and the advances have been important. Nowadays, it is possible to do quantitative predictions with chemical accuracy for middle-size molecules, and some type of calculations, especially density functional-based methodologies, are routinely done in many chemical laboratories. One very important aspect on the influence of quantum theory in chemistry is the one of understanding. There are many chemical concepts which can be understood only through the laws of quantum mechanics. This chapter is about conceptual understanding and is not about the other very important issue of computing with chemical accuracy. 

Lakatos, B. and E. Varga (1988). Probability density functions based micromixing model of chemical reactors. Computers in Chemical Engineering 12, 165-169. 

As a consequence of the size limitations of the ab initio schemes, a large number of more-approximate methods can be found in the literature. Here, we mention only the density functional-based tight binding (DFTB) method, which is a two-center approach to DFT. The method has been successfully applied to the study of proton transport in perov-skites and imidazole (see Section 3.1.1.3). The fundamental constraints of DFT are (i) treatment of excited states and (ii) the ambiguous choice of the exchange correlation function. In many cases, the latter contains several parameters fitted to observable properties, which makes such calculations, in fact, semiempirical. 

Density functional-based theoretical methods have been demonstrated to give highly accurate predictions of nitrenium ions structures, singlet-triplet energy gaps, and vibrational spectra. Future challenges in the area of theoretical predictions include the accurate modeling of nitrenium ion reactions and reaction rates. 

Frauenherm, T.. Seifert, G., Elstner, M., Hajnal, Z., Jungnickel. G.. Porezag. D.. Suhai. S.. and Scholz. R. 2000. A Self-consistent Charge Density-functional Based Tight-binding Method for Predictive Materials Simulations in Physics, Chemistry and Biology , Phys. Stat. Sol. B. 217. 41. 

N. Choly et al Multiscale simulations in simple metals A density-functional-based methodology. Phys. Rev. B 71, 094101 (2005)... 

AMI Semiempirical Austin method 1 CSA Conformational space annealing DFT Density functional theory DFTB Density-functional-based tight binding EA Evolutionary algorithm... 

In 1995-96, Scott Boesch provided the first tests of various density functional-based quantum chemical methods for calculating the structures, vibrations, and spin properties of p-benzoquinones and their semiquinone radical anions.(5 -56) Although several DF-based methods give comparably accurate... 

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