Tight-binding simulations of argon cation clusters

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Abstract
A simple, semiempirical model was used to study the ground and excited state properties of argon cation clusters at 60 K. The model is a tight-binding Hamiltonian whose parameters are determined from atomic and diatomic properties. Monte Carlo simulations were used to calculate the average properties of these clusters. The photoabsorption spectrum was in good agreement with previous calculations and experiments. The splitting of the photoabsorption spectrum for clusters with greater than 14 atoms was investigated. The two excited states corresponding to the splitting arise from a 3-atom ion core, perturbed by a 4th atom, with solvation from the remaining atoms. The perturbation of the 3-atom ion core by the 4th atom is of the form ψion core±ψ4. The splitting can be decomposed into a contribution solely from the 4 atom wave functions (75% of the splitting) and to additional solvation stabilization of the low energy excited state over the high energy excited state (25%).