PRINCIPAL COMPONENTS OF IONICITY

Conventionally, numerical values of effective partial charges are assigned to atoms in molecules and crystals in order to economically describe the ionicity or polarity of chemical bonds. However, quite different values are obtained when applying the various experimentally or theoretically based recipes or definitions of atomic charges. A factor analysis has been performed on atomic partial charge values from about two dozen different approaches. Only a single principal component of ionicity has been found, which is common to all the various operational charge definitions. It covers more than 90% of the variances. Apart from quite different scale units, the remaining discrepancies between different charge scales are due to individual factors for every charge recipe.