Does solvation cause symmetry breaking in the I3− ion in aqueous solution?

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Abstract
We seek to answer the question posed in the title by simulation of the tri-iodide ion in water, modeling the intermolecular interactions by classical potentials. The decrease in solvation free energy as a function of the dipole moment of the ion is calculated using an extended dynamics simulation method. This decrease is approximately quadratic in the ion dipole. Symmetry breaking occurs if this decrease is greater than the energy required to polarize the ion. We use ab initio calculations on an isolated ion to find the electronic and vibrational contributions to the polarizability, from which the polarization energy can be calculated. The solvated ion is found to be more stable when displaced along the asymmetric stretching coordinate, due to contributions of this deformation to the molecular dipole. As a test of the model’s reliability, it is used to derive solvation force autocorrelation functions from which time scales for vibrational energy and phase relaxation are estimated. The results are demonstrated to agree well with experimentally obtained values for these phenomena, vindicating reliability of the theoretical approach.