Semiempirical implementations of the EHCF paradigm

In the context of the EHCF construct described in the previous section, the problem of semiempirical modeling of TMCs electronic structure is seen in a perspective that is somewhat different from that of the standard HFR MO LCAO-based setting. The EHCF provides a framework which implicitly contains the crucial element of the theory the nonvanishing cumulant of the two-electron density matrix related to the cZ-shell. Instead of hardly systematizeable attempts to catch qualitative features of 

Further evaluations [164,165] have demonstrated the applicability of the fitted system of parameters for calculations of the electronic structure and spectra of numerous complexes of divalent cations using merely the CNDO parametrization for the /-system. In [140,169] the EHCF method is also extended for calculations of the ligands by the INDO, MINDO/3, and SINDO/1 parametrizations. In all calculations the experimental multiplicity (spin) and spatial symmetry of the corresponding ground stales were reproduced correctly. The summit of this approach has been reached in [170] by calculations on the i.s-[Fe(NCS btbipyjo] complex. Its molecular geometry is known both for the HS and LS isomers of the said compound. The calculation 

CLASSICAL MODELS OF MOLECULAR STRUCTURE MOLECULAR MECHANICS 

---