Interacting Quantum Atoms Analysis of the Reaction Force: A Tool to Analyze Driving and Retarding Forces in Chemical Reactions

The analysis of the reaction force and its topology has provided a wide range of fruitful concepts in the theory of chemical reactivity over the years, allowing to identify chemically relevant regions along a reaction profile. The reaction force (RF), a projection of the Hellmann‐Feynman forces acting on the nuclei of a molecular system onto a suitable reaction coordinate, is partitioned using the interacting quantum atoms approach (IQA). The exact IQA molecular energy decomposition is now shown to open a unique window to identify and quantify the chemical entities that drive or retard a chemical reaction. The RF/IQA coupling offers an extraordinarily detailed view of the type and number of elementary processes that take reactants into products, as tested on two sets of simple reactions. The coupling of Reaction Force and Interacting Quantum Atoms methodologies is presented as a powerful tool to identify driving and retarding forces in chemical reactions in order to be used in a rational design framework by tuning the activation energies. The RF/IQA coupling offers a feasible way to characterise the different elementary processes along a reaction coordinate, which has been tested in two types of reactions: (i) proton transfer (bond‐breaking/forming) and (ii) cis‐trans isomerisation (no bond‐breaking/forming).