ABSTRACT
It would have been easier to put vague and intuitive concepts on a firmer quantum mechanical footing if they had not been so successful. Indeed, one can only admire the amount of interpretation and prediction accomplished by chemists using their toolbox of concepts. Some of these ‘‘toolbox users’’ may be distrustful of theoretical chemists trying to fix something that, according to these users, is not
broken [5]. On the other hand, chemistry does need the input of quantum mechanics for a different reason. Chemists want to fundamentally understand why a chemical bond between the two same atoms is so similar in different molecules and why molecules in a homologous series behave in such a similar way, for example.
