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• 作者：Robert Q. Topper ; William V. Feldmann ; Isaac M. Markus ; Denise Bergin ; Paul R. Sweeney
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：September 29, 2011
• 年：2011
• 卷：115
• 期：38
• 页码：10423-10432
• 全文大小：944K
• 年卷期：v.115,no.38(September 29, 2011)
• ISSN：1520-5215

文摘

Simulated annealing Monte Carlo conformer searches using the 鈥渕ag-walking鈥?algorithm are employed to locate the global minima of molecular clusters of ammonium chloride of the types (NH₄Cl)_n, (NH₄⁺)(NH₄Cl)_n, and (Cl^{鈥?/sup>)(NH₄Cl)_n with n = 1鈥?3. The M06-2X density functional theory method is used to refine and predict the structures, energies, and thermodynamic properties of the neutral, cation, and anion clusters. For selected small clusters, the resulting structures are compared to those obtained from a variety of models and basis sets, including RI-MP2 and B3LYP calculations. M06-2X calculations predict enhanced stability of the (NH₄+)(NH₄Cl)_n clusters when n = 3, 6, 8, and 13. This prediction corresponds favorably to anomalies previously observed in thermospray mass spectroscopy experiments. The (NH₄Cl)_n clusters show alternations in stability between even and odd values of n. Clusters of the type (Cl鈥?/sup>)(NH₄Cl)_n display a magic number distribution different from that of the cation clusters, with enhanced stability predicted for n = 2, 6, and 11. None of the observed cluster structures resemble the room-temperature CsCl structure of NH₄Cl(s), which is consistent with previous work. Numerous clusters have structures reminiscent of the higher-temperature, rock-salt phase of the solid ammonium halides.}