On non-negativity of Fukui function indices

In this paper we have analyzed the factors which cause Fukui function (FF) indices to be negative, when evaluated in condensed form through crude finite difference approximation. Inability to take care of the relaxation effect and improper charge partitioning techniques have been cited to be the probable reasons. For the first time, we have shown that the "stockholders'' charge partitioning technique (i.e., Hirshfeld's analysis) produces non-negative FF values which, when evaluated through other kinds of charge partitioning techniques, become negative in some cases. Advantages of "stockholders'' charge partitioning over other kinds of partitioning techniques are also discussed, particularly in case of evaluation of condensed FF. (C) 1999 American Institute of Physics. [S0021-9606(99)30617-6].