Calculating Entropies of Large Molecules in Aqueous Phase

Abstract

Entropy benchmarking of different sized molecules in aqueous phase is carried out for known solvation models, where we compare geometry and solvation cavity packing parameters, which allows us to improve the accuracy of the obtained entropy values using empirical corrections. A comparison of solvation entropy models is conducted for a benchmarking set of 56 molecules, showing how an accurate description of cavitation entropy and its hindrance on other entropy values is important for large-sized solute molecules. Finally, we compare reaction free energies with entropies calculated using the most accurate solvation model considered, where we demonstrate a significant improvement in the accuracy relative to experimental values.

Ab Initio Investigation of Covalently Immobilized Cobalt-Centered Metal–Organic Catalysts for CO2 Reduction: The Effect of the Substrate on the Reaction Energetics

“…There is no simple method for calculating solvation entropy components (shown in eq ) such as cavitational entropy for immobilized catalysts on a substrate without doing computationally expensive molecular dynamics calculations. For small free molecules, such as CO and CO 2 , vibrational entropy by itself significantly underestimates the entropy contribution . However, in Figure , the vibration free energy reaction pathway (shown in green) is calculated using only vibrational entropy components.…”

“…In particular, vibration entropy is used to calculate free energies of the substrate immobilized CoPc/CoTPP systems, and solvation entropy (which also includes vibration entropy as one of its components, see eq ) is used to calculate free energies of the small intermediate molecules such as CO and CO 2 . For homogeneous CoPc/CoTPP in Figures and and intermediates such as CO, CO 2 , H 2 O, and H 2 , solvation entropies have been calculated using water as the solvent. , …”

Towards understanding solvation effects on the conformational entropy of non-rigid molecules

“…3,5 While conformational changes (in solution) also affect the translational, vibrational, and rotational partition functions, their influence on the absolute molecular entropy cannot be described exclusively by these terms. [24][25][26][27] Only the conformational entropy reflects the overall PES change and provides a distinctive way for investigating changes of the absolute molecular entropy upon solvation.…”

“…35,36 Cavity terms also typically account for rotational and translational entropy hindrances of the solute due to the surrounding solvent molecules. 26 Thus, our protocol allows for a discrete treatment of the conformational part of the entropy, separate from configurational or ''orientational'' entropies 37,38 due to solvent-solute interaction. If the latter are of interest, other models such as the grid inhomogeneous solvation theory (GIST) should be employed.…”

“…For a more comprehensive investigation of these aspects see, e.g., the recent work of Conquest and Stampfl. 26 Their benchmark study furthermore reviews corrections to solvent-excluded surface or cavity entropy terms and the steps necessary to obtain accurate molecular entropies in solution.…”