  A generalization of the density-functional based tight-binding method (DFTB)
for the use with range-separated exchange-correlation functionals is presented.
It is based on the Generalized Kohn-Sham (GKS) formalism and employs the
density matrix as basic variable in the expansion of the energy functional, in
contrast to the traditional DFTB scheme. The GKS-TB equations are derived and
appropriate integral approximations are discussed in detail. Implementation
issues and numerical aspects of the new scheme are also covered.
