DFTB method functional-based tight-binding

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

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. 

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... 

A self-consistent charge density functional based tight binding (SCC-DFTB) method was used for the calculations of the geometries, electronic... 

A compromise between computational effort and accuracy can be readied within an approximate KS-DFT scheme - a density functional based tight-binding (DFTB) method. This approximation assumes very strong atomic potential so that different atomic orbitals barely overlap. It can be considered the analog of the standard linear combination of atomic orbital (LCAO) approach with an LCAO representation of the KS orbitals. Like the LCAO approach, the atomic locations can be specified arbitrarily, so the method can be applied to nonperiodic (noncrystalline) materials. The fundamental step of the DFTB... 

Somewhat removed is the density functional based tight-binding method (DFTB), which is based on a second-order expansion of the Kohn-Sham total energy, employing a self-consistent redistribution of Mulliken charges (SCC-DFTB) (Elstner et al. 1998). It also employs dispersion corrections similar to the DFT-D method and has successfully been applied, e.g., to nuclear-base stacking problems (Elstner et al. 2001). 

Methods particularly devoted to biomolecular processes are more frequently used than multipurpose semi-empirical molecular orbital methods like AMI and PM3. Self-consistent-charge density functional theory based tight-binding (SCC-DFTB), an efficient method derived from density functional theory, is well adapted for QM/MM studies of biomolecular systems."... 

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. 

Molecular dynamics methods based on quantum chemical calculations to compute the energy of a cluster as a function of the nuclei positions avoid the difficult task of building an intermolecular potential. Tight-binding molecular dynamics, semiempirical and Hartree-Fock ab initio Born-Oppenheimer dynamics, Car-Parrinello DFT molecular dynamics, and ADMP molecular dynamics are becoming more and more popular. The more sophisticated techniques are still Hmited to the study of clusters over short simulation times (ps time scale). The tight-binding approach SCC-DFTB is cheap and appears to be quite accurate. 

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