It is safe to say that there is no consensus regarding the optimal choice PFT�� ic50 of method
when one considers additionally the prediction of energies for electronically distinct states of the same species, such as those arising from different electronic configurations of a metal center, from a different distribution of oxidation states within a metal cluster, or even from the interplay between metal-centered and ligand-centered redox processes. When these factors come into play, the error margin can easily exceed by far the optimistic range mentioned earlier. Nevertheless, even if the estimated errors may be already too large for quantitative predictions in cases of small activation energies such as those observed during the catalytic cycle of the OEC (Sproviero et al. 2007), the simulation of reaction pathways is a fundamentally important application of DFT. A representative example that stands out in the field of photosynthesis research is the systematic work that has been focused on elucidating mechanistic aspects in the catalytic cycle of OEC (Lundberg and Siegbahn 2004; Siegbahn 2006a, 2008a, b; Sproviero et al. 2008a,
b). This line of work demonstrates that DFT calculations can offer significant input to mechanistic investigations, Blasticidin S molecular weight sometimes revealing possibilities that were not previously considered. It should be kept in mind, however, that a reaction mechanism predicted by DFT cannot be validated on the basis of computed energies alone, especially when the structure of the principal component is itself debatable. All such efforts should attempt to combine and incorporate many lines of evidence, taking into account additional criteria such as the spectroscopic properties
of the putative intermediates. Vibrational frequencies Closely connected in research practice to the procedure of structural optimization is the calculation of vibrational frequencies. They are used not only for simulating Tariquidar infrared (IR) or Raman spectra but Methocarbamol also for characterizing the nature of stationary points as minima or transition states. Moreover, the information obtained from such a calculation is used to compute statistical thermodynamic corrections to the electronic energy and thus to make direct comparisons with experimentally determined free energies. It is well established that the predicted harmonic frequencies with GGA functionals such as BP86 and PBE typically agree well with measured vibrational fundamentals if basis sets of polarized triple-ζ quality are used (Murray et al. 1992; Sosa et al. 1992; Stratmann et al. 1997).