A new approach to local hardness

Abstract

The applicability of the local hardness as defined by the derivative of the chemical potential with respect to the electron density is undermined by an essential ambiguity arising from this definition. Further, the local quantity defined in this way does not integrate to the (global) hardness - in contrast with the local softness, which integrates to the softness. It has also been shown recently that with the conventional formulae, the largest values of local hardness do not necessarily correspond to the hardest regions of a molecule. Here, in an attempt to fix these drawbacks, we propose a new approach to define and evaluate the local hardness. We define a local chemical potential, utilizing the fact that the chemical potential emerges as the additive constant term in the number-conserving functional derivative of the energy density functional. Then, differentiation of this local chemical potential with respect to the number of electrons leads to a local hardness that integrates to the hardness, and possesses a favourable property; namely, within any given electron system, it is in a local inverse relation with the Fukui function, which is known to be a proper indicator of local softness in the case of soft systems. Numerical tests for a few selected molecules and a detailed analysis, comparing the new definition of local hardness with the previous ones, show promising results.

30 pages (including 6 figures, 1 table)

References in corpus (5)

• The mathematics of functional differentiation under conservation constraint
• Derivative of the Lieb definition for the energy functional of density functional theory with respect to the particle number and the spin number
• On the thermodynamical analogy in spin-polarized density functional theory
• Differentiation of functionals with variables coupled by constraints: Analysis through a fluid-dynamical model
• Stability of equilibrium under constraints: Role of second-order constrained derivatives

Cited by in corpus (2)

• Why the traditional concept of local hardness does not work
• Local energy: a basis for local electronegativity and local hardness