Comment on "Revisiting the definition of local hardness and hardness kernel" by C. A. Polanco-Ramirez, M. Franco-Pérez, J. Carmona-Espíndola, J. L. Gázquez and P. W. Ayers, Phys. Chem. Chem. Phys., 2017, 19, 12355.

In a recent article Polanco-Ramirez et al. proposed new definitions of local chemical potential and local hardness starting from the first derivative of the energy with respect to the number of electrons and a smart use of the chain rule. In this comment we show that this derivation appears naturally in the Taylor expansion of the energy, showing that the construction of Polanco-Ramirez et al. is not artificially built.