Cooperative effects in the structuring of fluoride water clusters: Ab initio hybrid quantum mechanical/molecular mechanical model incorporating polarizable fluctuating charge solvent

Abstract

A new hybrid quantum mechanical/molecular mechanical model of solvation is developed and used to describe the structure and dynamics of small fluoride/water clusters, using an ab initio wave function to model the ion and a fluctuating charge potential to model the waters. Appropriate parameters for the water–water and fluoride–water interactions are derived, with the fluoride anion being described by density functional theory and a large Gaussian basis. The role of solvent polarization in determining the structure and energetics of F(H2O)4− clusters is investigated, predicting a slightly greater stability of the interior compared to the surface structure, in agreement with ab initio studies. An extended Lagrangian treatment of the polarizable water, in which the water atomic charges fluctuate dynamically, is used to study the dynamics of F(H2O)4− cluster. A simulation using a fixed solvent charge distribution indicates principally interior, solvated states for the cluster. However, a preponderance of trisolvated configurations is observed using the polarizable model at 300 K, which involves only three direct fluoride–water hydrogen bonds. Ab initio calculations confirm this trisolvated species as a thermally accessible state at room temperature, in addition to the tetrasolvated interior and surface structures. Extension of this polarizable water model to fluoride clusters with five and six waters gave less satisfactory agreement with experimental energies and with ab initio geometries. However, our results do suggest that a quantitative model of solvent polarization is fundamental for an accurate understanding of the properties of anionic water clusters.

Coupling a polarizable water model to the hydrated ion–water interaction potential: A test on the Cr3+ hydration

“…This problem has been addressed by including three-and four-body terms, as well as the use of polarizable water models, and quite reasonable results have been obtained on singly charged cations. [17][18][19][20][21][22][23][24] In the case of doubly charged ones, a clear improvement is observed, [25][26][27][28][29][30][31] especially on structural parameters. Furthermore, for several lanthanide ions ͑Ln 3ϩ ͒ in aqueous solutions, Kowall et al 32 applied a polarizable water model that enables the description of the decrease in the water-exchange rate, Ln-O distance ͑''lanthanide contraction''͒ and the coordination number along the series.…”

Empirical force fields for biological macromolecules: Overview and issues

“…50,[55][56][57][58]60,[73][74][75] In many of these models there was an increased ability to more accurately treat changes in properties, such as the density as a function of temperature, compared to additive water models. Other examples where the inclusion of electronic polarization has lead to improvements in the modeling of molecular interactions includes the solvation of ions, 54,61,70,76 ion-pair interactions in micellar systems, 77 condensed phase properties of a variety of small molecules, 60,65,78 -81 cation-interactions, 82 and in interfacial systems. 83 However, although application of polarization to small molecules has made progress, developments in the area of biomacromolecular force fields have been limited.…”

Development of first-principles interaction model potentials. An application to the study of the bromide hydration

“…31,32,[41][42][43]68 Moreover, the number of possible structures increases with the size of the cluster, 30,68,91 due to the significant role played by the water-water interactions. In order to guarantee an adequate prospecting, numerical energy minimizations using different strategies were carried out.…”