(3.1.4) Adamo and Ciofini : The terms "empirical" and "nonempirical" used above deserve some clarification. For us, the term "nonempirical" denotes those DFAs whose internal coefficients are not determined by an error minimization relative to external reference data sets (experimental or theoretical), but instead are fixed using only constraints derived by theory. The term "empirical" denotes, by contrast, those functionals whose coefficients are determined by a parameterization procedure. However, since these latter functionals may also respect some theoretical constraints, we prefer to use the term "semiempirical" to underline their theoretical foundation. In our opinion, these two terms, "nonempirical" and "semiempirical", are not measures of quality, but rather indicate how the functional has been developed. Between these two classes, the term "minimally parameterized" is also used, to underline that an effort has been made to reduce the number of functional parameters, as mentioned above.