engleski

Minimal requirements for approximate wavefunctions of molecules

It is shown that diamagnetic shielding σd and diamagnetic susceptibility χ d provide necessary but not sufficient conditions which approximate molecular wavefunctions should satisfy. Hence they represent minimal requirements for acceptable qualitative description of electrons in molecules. Some current semiempirical methods are examined by using σ d and χ d tests. It appears that the MINDO/3 and MNDO schemes do not perform well for N, O and F atoms. The origin of discrepancies in the calculated σ d values lies in the use of inadequate orbital screening constants ξ. The role of other one-electron properties in improved parametrization of the semiempirical procedures is briefly discussed.

semiempirical methods; diamagnetic shielding; molecular wavefunctions

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