Strong and Weak Points of NDDO Semiempirical Methods

Pulay s converger should also not be routinely used in following reaction paths, as the lowest energy path may involve intersystem crossing. Pulay s converger will ensure that changes in the electronic wavefunction are minimized, i.e., it will ensure that even when intersystem crossing should occur, the form of the initial wavefunaion will be preserved. 

This converger almost never fails, but because of its complexity it is seldom used. It should be reserved for recalcitrant systems for which all other methods have failed. 

At the present time, it is safe to say that proportionally very few systems are known that fail to converge when one or more of these convergers are used. 

STRONG AND WEAK POINTS OF NDDO SEMIEMPIRICAL METHODS 

As was mentioned in the introduaion, a comprehensive survey of semiempirical methods and MNDO in particular has recently been written by Thiel. In it he rigorously describes the reladonship between semiempirical and ab initio methods. His survey summarizes the applicadons of MNDO to the study of chemical reaction. Thiel is the author of the MNDOC method, a correlated form of MNDO he describes the relationship of this method to other semiempirical methods. Since his survey includes very effecdvely the current status of semiempirical mediods, a similar review is redundant, and interested readers are referred to Thiel s work. 

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Strong and Weak Points of NDDO Semiempirical Methods 61... 

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