A Free Energy Decomposition Analysis: Insight into Binding Thermodynamics from Absolutely Localized Molecular Orbitals

Traditional energy decomposition analysis (EDA) methodscan providean interpretive decomposition of non-covalent electronic binding energies.However, by definition, they neglect entropic effects and nuclearcontributions to the enthalpy. With the objective of revealing thechemical origins of trends in free energies of binding, we introducethe concept of a Gibbs decomposition analysis (GDA) by coupling theabsolutely localized molecular orbital treatment of electrons in non-covalentinteractions with the simplest possible quantum rigid rotor-harmonicoscillator treatment of nuclear motion at finite temperature. Theresulting pilot GDA is employed to decompose enthalpic and entropiccontributions to the free energy of association of the water dimer,fluoride-water dimer, and water binding to an open metal sitein the metal-organic framework Cu(I)-MFU-4l. The results show enthalpic trends that generally track the electronicbinding energy and entropic trends that reveal the increasing priceof loss of translational and rotational degrees freedom with temperature.

Automated summary

Traditional energy decomposition analysis (EDA) methods can explain the decomposition of non-covalent electronic binding energies, but they neglect entropic effects and nuclear contributions to the enthalpy. In order to reveal the chemical origins of trends in free energies of binding, we introduce the concept of a Gibbs decomposition analysis (GDA). By coupling the absolutely localized molecular orbital treatment of electrons in non-covalent interactions with the simplest possible quantum rigid rotor-harmonic oscillator treatment of nuclear motion at finite temperature, we can decompose enthalpic and entropic contributions to the free energy of association. The results show enthalpic trends that generally track the electronic binding energy and entropic trends that reveal the increasing price of loss of translational and rotational degrees freedom with temperature.