Ambiguities in solvation free energies from cluster-continuum quasichemical theory: lithium cation in protic and aprotic solvents

Abstract

Li cation solvation free energies were calculated in 10 solvents using the cluster-continuum quasichemical theory. The best agreement with experimental-based “bulk” scale values was achieved for the “monomer” cycle predictions.

Cluster-Continuum Model as a Sanity Check of Sodium Ions’ Gibbs Free Energies of Transfer

“…According to the high-quality DLPNO-CCSD­(T)-based Feller–Peterson–Dixon approach applied in conjunction with the SMD continuum model and msRRHO thermochemistry, all clusters Na + (S) n are thermodynamically unstable in the liquid phase for n > 5. These clusters with large n numbers are fragmentized into the species with smaller n and liberate one or several solvent molecules S. The same is true for Li + (S) n clusters . These findings, complemented with the usage of the monomer instead of the cluster cycle in cluster-continuum models, substantially reduce the conformational issues that are now a bottleneck of the whole MC CCM approach.…”

“…several solvent molecules S. The same is true for Li + (S) n clusters. 49 These findings, complemented with the usage of the monomer instead of the cluster cycle in cluster-continuum models, substantially reduce the conformational issues that are now a bottleneck of the whole MC CCM approach. This is because neither general force field nor semiempirical methods 112 guarantee reliable conformational distribution requiring DFT optimizations with subsequent continuum model single-point energy evaluations on many energetically and structurally diverse geometries.…”

“…37 This is due to the problems related to an accurate description of the solvent molecular clusters, including severe conformational issues and inaccurately predicted solvation free energies from the most widely used dielectric continuum models. 39,49 Subsequently, we restrict ourselves only to the monomer cycle cluster-continuum model in this work.…”

“…We have recently shown that the monomer cycle cluster-continuum model (MC CCM), where infinitely separated molecules are the solvent initial state, is preferred over the cluster cycle (CC CCM) counterpart where the molecular cluster is used as an initial state . This is due to the problems related to an accurate description of the solvent molecular clusters, including severe conformational issues and inaccurately predicted solvation free energies from the most widely used dielectric continuum models. , Subsequently, we restrict ourselves only to the monomer cycle cluster-continuum model in this work.…”

Physical and numerical aspects of sodium ion solvation free energies via the cluster-continuum model

“…Despite the cluster-continuum model has been successfully applied earlier to study Li + solvation, 30,34,35,39,40 its applications for Na + in non-aqueous solutions are less numerous. 34,41,42 In their recent review, Pliego and Riveros suggest that the sodium ion solvation free energies obtained within the cluster continuum approach are less accurate than their lithium counterparts.…”