CaO和MgO团簇和团簇离子的结构和稳定性：实验质谱的另一种解释
Structures and Stabilities of CaO and MgO Clusters and Cluster Ions: An alternative interpretation of the experimental mass spectra
摘要：
用{ \em ab initio}微扰离子加极化方法研究了双电荷非化学计量（CaO）$_n$ Ca $^{2+}$（n=1- 29）团簇离子和中性化学计量（MgO）$_n$和（CaO）$_n$（n= 3，6，9，12，15，18）团簇离子的结构和相对稳定性.氧化物阴离子的大的配位依赖极化率有利于表面位点的形成，使得具有本体配位的阴离子首先出现的临界簇尺寸大于在碱金属卤化物的相关情况下发现的临界簇尺寸。因此，我们表明，碱金属卤化物和碱土金属氧化物簇离子之间有很大的结构差异，相反，在实验质谱的相似性所建议的。氧化物的情况下，幻数的另一种解释，这涉及到明确考虑异构体结构不同的基态。与以前研究的（MgO）$_n$镁$^{2+}$簇离子的比较表明，块状结构性能的出现与尺寸是缓慢的氧化钙。然而，两种材料的双电荷团簇的结构是相当相似的。相反，中性物的研究揭示了MgO和CaO之间有趣的结构差异，类似于碱金属卤化物的情况。
英文摘要：
The structures and relative stabilities of doubly-charged nonstoichiometric (CaO)$_n$Ca$^{2+}$ (n=1--29) cluster ions and of neutral stoichiometric (MgO)$_n$ and (CaO)$_n$ (n=3,6,9,12,15,18) clusters are studied through {\em ab initio} Perturbed Ion plus polarization calculations. The large coordination-dependent polarizabilities of oxide anions favor the formation of surface sites, making the critical cluster size where anions with bulk coordination first appear larger than that found in the related case of alkali halides. Thus, we show that there are substantial structural differences between alkali halide and alkaline-earth oxide cluster ions, contrary to what is suggested by the similarities in the experimental mass spectra. An alternative interpretation of the magic numbers for the case of oxides is proposed, which involves an explicit consideration of isomer structures different from the ground states. A comparison with the previously studied (MgO)$_n$Mg$^{2+}$ cluster ions shows that the emergence of bulklike structural properties with size is slower for calcium oxide. Nevertheless, the structures of the doubly charged clusters are rather similar for the two materials. On the contrary, the study of the neutrals reveals interesting structural differences between MgO and CaO, similar to those found in the case of alkali halides.
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