On the determination of bond lengths by ab-initio methods II: Simplifications and new considerations

This work analyzes some improvements and simplifications made on procedures to calculate molecular bond lengths, through the combination of different theoretical methods that we have proposed some time ago. The main improvement that we have presently achieved lies in the combined application of the two procedures already presented, one related to the reduction of systematic errors and the other associated to the reduction of random errors. A second part of the work is devoted to explore the possibility to abbreviate the procedure to reduce random errors, either by reducing the basis set size in ab-initio methods or by modifying the parametrization in semiempirical methods. Finally, we present a first attempt of developing a INDO-like method specifically parametrized to obtain bond lengths, suitable to be successfully combined with the well known PM3 semiempirical method.