On the Question of Empirical Corrections in Ab Initio Model Chemistries

Model chemistries that employ additivity schemes have become increasingly popular within the chemical community. These approaches are predicated upon the assumption that less rigorous (and, therefore, less expensive) calculations may be combined to approximate a more accurate (and otherwise intractable) level of theory. Most of these models make some use of an empirical correction, the desirability of which is at best questionable. The present paper critically examines the importance of one such correction (the “higher-level correction”) to the most widely used additivity method (the Gaussian model). An alternative approach, which does not depend upon any sort of ad hoc empiricism, is also outlined. The current model is found to offer accuracy comparable to that of the Gaussian model.