Some relationships within the nonlocal (pair-site) chemical reactivity formalism of density functional theory

General and exact relationships within the nonlocal (pair-site) reactivity context are explicitly derived in the framework of density functional theor y. The equations are expressed in terms of linear response functions and as sociated kernels of the Fukui function and its derivatives with respect to the electron number at constant external potential. It is shown that under a local approximation for the general nonlocal pair-site kernels, the nonlo cality character of the chemical response must appear only implicitly throu gh the changes in the chemical potential of the system. In the framework of a more general nonlocal reactivity theory, new relations can be written th rough the incorporation of more spatial coordinates. The case of a three-si te equation between Fukui functions has been explored. (C) 2000 American In stitute of Physics. [S0021- 9606(00)30648-1].