Extended Huckel method overlap matrix

Pyykko and coworkers have formulated a relativistic extended Huckel method for molecules. This method incorporates relativistic effects by a systematic parametrization using Desclaux s atomic relativistic Dirac-Fock calculation. The Dirac-Fock atomic energies and the off-diagonal elements are proportional to the product of the overlap matrix element in the relativistic lsjm basis. Pyykko and coworkers - have applied this method to a number of molecules. 

We will now continue the discussion using the Extended-Huckel related tight-binding method, which is identical to the Huckel method as it is called by organic chemists. In it, the overlap matrix elements are approximated as ... 

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