Abstract
We present a thermodynamic perspective of the microsolvation of ions by rare gas atoms, which is based on parallel tempering Monte Carlo (PTMC) simulations. This allows the establishment of a clear relationship between the structure of the solvation shells and the heat capacity (CV) as a function of the number of individual solvent species. The dependence of CV on the temperature allows the identification of the internal structure rearrangements and the onset of partial or total melting of the clusters. As an application, we have employed the PTMC technique to study the thermodynamic properties of clusters resulting from the microsolvation of Li+ by argon atoms. Specifically, calculations have been carried out for the clusters Li+Arn (n = 4-18, 33, 34, and 38) by applying two different potential energy surfaces (PESs): one includes only two-body interactions, while the other also incorporates three-body contributions. Whenever possible, we compare the present thermodynamic results with global optimization studies carried out previously (F. V. Prudente, J. M. C. Marques and F. B. Pereira, Phys. Chem. Chem. Phys., 2017, 19, 25707; W. S. Jesus et al., Int. J. Quantum Chem., 2019, 119, e25860). We conclude that the melting process arises for lower temperatures when the model PES accounts for three-body interactions. Additionally, we characterize the melting processes of the first and second solvation shells. For some specific clusters, structural rearrangements of the most external argon atoms are observed at very low temperatures.
Highlights
Solvation plays a fundamental role in a great variety of phenomena within the broad area of physical chemistry
We present a thermodynamic perspective of the microsolvation of ions by rare gas atoms, which is based on parallel tempering Monte Carlo (PTMC) simulations
We show by the present work that results for the heat capacity as a function of temperature present distinct features for the two potential energy surfaces (PESs)
Summary
Solvation plays a fundamental role in a great variety of phenomena within the broad area of physical chemistry. One of the most cumbersome stages of the microsolvation study is the development of the relevant potential energy surface (PES) It implies the calculation of the interaction energy for several geometries at a high-level of theory, followed by a leastsquares fitting to an appropriate analytical function. Because of this difficulty in representing the accurate PES, theoretical insight on microsolvation has been acquired by using single-atom ions and atomic solvents. Cases involving solvation of alkali-metal ions with rare-gas atoms have been subjected to many theoretical and experimental studies [28,29,30,31,32,33,34,35]. We have performed global optimization studies for describing the microsolvation of Li+ by argon [36,37,38] and krypton 38, or a mixture of both 39
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