Semi-empirical electronic structure method limitations

In fact, none of these points is really so important in a semi-empirical method, because such methods are not designed for performing absolute calculations on single molecules, but rather for studying the trends of physical properties in a series of related compounds. Computational experience shows that the general picture of the electronic structure is not significantly altered whatever method may be chosen, as long as the parameters or the coordinate axes of orbitals are varied within reasonable limits. 

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