Temperature‐dependent approach to chemical reactivity concepts in density functional theory

Abstract The chemical reactivity concepts of density functional theory are studied through a unified view in the temperature‐dependent approach provided by the grand canonical ensemble. This procedure leads to a more general perspective that enriches our understanding of the behavior of the average energy and its derivatives with respect to the average number of electrons, provides alternative definitions for those quantities that are “ill defined” at zero temperature, and allows one to determine the relationships among reactivity concepts at any temperature. In particular, it has been found that at high temperatures the parabolic model for reactivity indicators may be justified through the electronic entropy term in the Helmholtz free energy, and that at nonzero temperatures there is an electronic heat capacity contribution to the average energy. In summary, the unified view of the temperature‐dependent approach is an important complement to the zero‐temperature formulation that clarifies fundamental issues therein.