The nanosolvation of two lithium ions is explored using a Stockmayer model for the solvent molecules. We determine the structures and classical thermodynamics of a cluster comprised of two lithium ions surrounded by one hundred Stockmayer point particles over a range of dipole moments, ranging to mimic Tetrahydrofuran (0.641 a.u.) and Nitromethane (1.404 a.u.). Optimization is performed with a Brownian algorithm at T=0 K. For a dipole moment of 0.641 a.u., a total of 566,000 optimizations are performed from 1000 distinct basin hopping walks. For a dipole moment of 1.404 a.u., 330,000 optimizations are performed from the same size basin hopping sample. This process has reproduced the global minimum for a sufficient number of basin hopping steps to provide confidence that results have converged. These minima are sorted, combined, and reoptimized for all values of the dipole moment over a 24-point grid. This strategy is called a parameter space sweep, and has been employed in the past for similar investigations [J. Chem. Phys. 121, 6226-39, (2004).]. We compare the Li+-Li+ distance in the global minima as a function of the dipole moment of the solvent cluster, and we observe a decrease in its value with increasing dipole moment, followed by a sharp increase for values larger than 1.371 a.u.

Minima estimates of a dilithium ion mixed stockmayer cluster

ACS Spring 2022

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