DFT Studies of Isolated Fragments of Large Biological Systems [Pg.86]

In this review, the DFT studies of biological systems are divided into two groups corresponding to different ways of addressing the second aforementioned issue. The first one [Pg.85]

Let us underline some similarities and differences between a field theory (FT) and a density functional theory (DFT). First, note that for either FT or DFT the standard microscopic-level Hamiltonian is not the relevant quantity. The DFT is based on the existence of a unique functional of ionic densities H[p+(F), p (F)] such that the grand potential Q, of the studied system is the minimum value of the functional Q relative to any variation of the densities, and then the trial density distributions for which the minimum is achieved are the average equihbrium distributions. Only some schemes of approximations exist in order to determine Q. In contrast to FT no functional integrations are involved in the calculations. In FT we construct the effective Hamiltonian p f)] which never reduces to a thermo- [Pg.807]

In a contrary to the DFT studies of isolated molecules, where there is a strong link between applications to biological systems and general developments in the theory of density functionals, approaches used for modeling properties of chemical molecules embedded in the biological microscopic environment combine developments in many fields. These fields include DFT, statistical physics, dielectric theory, and the theory of liquids. [Pg.108]

This reaction profile also illustrates one of the other important challenges in the study of transition metal systems, namely that the metal-containing active site often has several accessible spin states. Specifically in the case of Fe(IV)=0, the triplet, quintet, and septet spin states. Consequently, the reaction can, in principle, proceed on different electronic potential energy surfaces and it is necessary to test all possibilities when exploring a reaction surface. This has been labeled two-state reactivity and has been elaborated by Shaik, Schwarz, Schroder, and co-workers (36—40). In the case of TauD, the results show that the reaction is only feasible on the quintet surface, in agreement with earlier DFT studies (11,41 —45). [Pg.307]

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