engleski

Critical appraisal of some current semiempirical methods in calculating ESCA chemical shifts

Semiempirical MINDO/3 and MNDO methods are tested by calculating N(1s), O(1s), F(1s) and Si(2p) ESCA chemical shifts. Inner-shell binding energies (ISBE) are estimated by electrostatic potentials exerted at the host nuclei, computed in atomic monopole approximation (AMEP). Reorganization energy upon ionization is taken into account by the equivalent core model whenever possible. The calculated ESCA shifts are in moderately good agreement with experimental data. Comparison with earlier EHT, SCC-MO and CNDO/2 studies shows that the SCC-MO approach is the method of choice if ESCA shifts are to be calculated at the semi-empirical level, as this approach gives a better description of the electron charge distribution in molecules, and in particular gives better estimates of atomic monopoles. It is suggested that ESCA shifts should be used in the empirical adjustment of parameters in semiempirical methods.

semiempirical methods ; chemical shift

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