A coupling between the equilibrium state variables of open molecular and reactive systems

Abstract

The charge sensitivity approach, based upon the hardness/softness reactivity descriptors originating from density functional theory, provides a useful framework for an analysis of the ground-state couplings between the geometrical and/or populational degrees of freedom of open molecular or reactive systems. Recent advances in this field are surveyed. The topics discussed cover the minimum-energy mapping transformations, which monitor the coupling between the electronic and geometrical structure parameters, the finite-difference analysis of the molecular hardness dependence on the system geometry, the implications of the integral Hellmann–Feynman theorem for trends in the ground-state energy differences, and the charge sensitivities of the externally open reactants. The algorithm for determining the minimum-energy transformations between the atomic electron populations (or net charges) and the nuclear positions in the open molecular system is proposed within the charge sensitivity analysis. The finite-difference approach is used to approximate the third-order derivative of the system ground-state energy, coupling the molecular hardness and the external potential due to the nuclei. The basic derivatives determining the quadratic Taylor expansion of the energy differences in the open molecular systems are explored and the concept of the transition Fukui function is introduced, which correlates changes in the energy difference between the two system geometries, due to displacements in the overall number of electrons of the system. The effective chemical potentials, hardness, softness and Fukui function quantities of the simultaneously open reactants are investigated and the results are interpreted in terms of the generalized Le Châtelier principle.