The Applicability of Point-Charge Approximations to the Calculation of Molecular Expectation Values
نویسندگان
چکیده
The recently developed self-consistent charge Xa (SCCXa) method has been utilised to investigate various types of point-charge approximations to molecular expectation values. In the first' A A part observables of the structure m 1 (r) r' Y L (r) and a1 (r) r -'1 Y L (r), respectively, are analysed yielding the conclusion that, in general, only certain matrix elements can be treated by point-charge approximations, namely the two-center crystal-field integrals and the three-center integrals. The results are then a<pplied to the calculation of the total valence energies as a function of bond distances, and it turns out that the SCC-Xo. method is able to reproduce equilibrium geometries with deviations of less than 100/o provided all matrix elements are evaluated in an exa'Ct way, while all investigated types of point-charge approximations fail in predicting geometries.
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