Parameter determination procedure for extended Hückel approximation and its application for solid-state electrolytes.

A determination procedure of transferable tight-binding parameters of extended Hückel approximation with charge self-consistency is explained, which is applicable to both molecules and crystalline solids. The parameters are adjusted by optimizing evaluation functions, compared with reference results of energy levels or band structure calculated by, for example, the density functional theory. By introducing the evaluation function, the automatic optimization of the parameters for small molecules and clusters is achieved, which makes it easy to determine an accurate parameter set and a wide application of the TB scheme. A practical procedure of parameter optimization is demonstrated for solid-state electrolytes of Li4GeS4 and Li3PS4.