Density-functional tight-binding DFTB method

Based on the previous implementation of the density functional tight-binding (DFTB) method in ALLCHEM, a hybrid DFT/DFTB method is currently under development. In the future this will be coupled to a molecular mechanics environment. 

In our subsequent studies on Aujv clusters we included a treatment of the electronic orbitals. For the calculation of the total energy of a given structure we used the parameterized density-functional tight-binding (DFTB) method of Seifert et al. For the determination of the structure of the lowest total energy we combined this method with genetic algorithms. We shall briefly discuss the results of the most extensive of those studies where Aujv clusters with N up to 58 were considered. ... 

Density Functional Tight-Binding (DFTB) Method... 

It is worth noting that when advanced QM methods cannot be used for the calculations, as in the case of large chromophores interacting with many water molecules, one possible approach is to use semiempirical models. For example, we showed that reliable solvatochromic shifts can be obtained using the Density Functional Tight Binding (DFTB) method [164, 165] in conjunction with PCM (see Table 17.1). 

MULTI-SCALE QM/MM METHODS WITH SELF-CONSISTENT-CHARGE DENSITY-FUNCTIONAL-TIGHT-BINDING (SCC-DFTB)... 

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. 

Cui Q, M Elstner, E Kaxiras, T Frauenheim, M Karplus (2001) A QM/MM implementation of the self-consistent charge density functional tight binding (SCC-DFTB) method. J. Phys. Chem. B 105 (2) 569-585... 

Cui, Q., Flstnee, M., Kaxieas, E., Feauenheim, T., Karplus, M., A QM/ MM Implementation of the Self-Consistent Charge Density Functional Tight Binding (SCC-DFTB) Method,... 

The resulting density functional-based tight binding (DFTB) method works well for homo-nuclear systems, where the charge transfer between the atoms in the system does not occur or is... 

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