Variational principles for describing chemical reactions. Reactivity indices based on the external potential

Area of Science:

• Theoretical Chemistry
• Quantum Chemistry
• Chemical Physics

Background:

• Variational principles analyzing electron density changes are key to understanding chemical reactivity.
• Previous work focused on electron density, but the impact of external potentials was less explored.

Purpose of the Study:

• To investigate the influence of external potentials on chemical reactivity.
• To develop new theoretical indices for quantifying molecular responses to external fields and chemical environments.

Main Methods:

• Extension of variational principles to include external potential effects.
• Definition of four novel reactivity indices: Upsilon, Xi, Lambda, and proton hardness (Pi).
• Application of these indices to model systems and reactions.

Main Results:

• The study defines a potential energy surface (Upsilon) based on external potential Taylor series.
• Introduces stabilization energy (Xi) and molecular flexibility (Lambda) at equilibrium.
• Defines proton hardness (Pi) analogous to chemical hardness for acid-base theory.

Conclusions:

• The new indices provide a framework for understanding molecular behavior under external potentials.
• These methods can be applied to diverse chemical phenomena, including molecular orientation and acid-base reactions.