On non-negativity of Fukui function indices. II

In this article we have tried to critically analyze the factors which cause the condensed Fukui function (FF) indices [f(r)] to attain a negative value in some cases. The evaluation of condensed FF indices needs finite-difference approximation to the electronic charge densities, and the finite-difference approximation needs partitioning of the electronic charge to the constituent atoms. In a previous article [J. Chem. Phys. 110, 8236 (1999)] we have argued that the probable factors, which cause the FF indices to appear negative in some cases, may be (i) the improper charge partitioning techniques adopted to evaluate f(r); (ii) large change in the electron number (Delta N = 1) when f(r) is evaluated in condensed form using the finite-difference approximation. In this article we want to focus more on the first factor. The present study shows through pictorial as well as numerical demonstrations of the charge-density difference [rho(neutral)((r) over bar)-rho(cation)((r) over bar) and rho(anion)((r) over bar)-rho(neutral)((r) over bar)] plots, how the negative condensed FF value appears with the use of improper charge partitioning and how the use of Hirshfeld partitioning can solve this problem. (C) 2000 American Institute of Physics. [S0021-9606(00)30128-3].