Ab initio tight binding

Empirical tight binding has proven to be very popular in recent years on ac count of its computational efficiency and accuracy. However, it has limitat ions, notably the difficulties associated with fitting parameters and impro ving models when the desired accuracy cannot be achieved. In the light of t his, a number of efforts have been made to derive tight-binding models from first principles. Here are described a number of formalisms based on densi ty functional theory which span the range of approaches currently being use d.