Department of Chemistry, The Centre for Theoretical and Computational Chemistry, 9037 Tromsø, Norway.
J Phys Chem A. 2012 May 31;116(21):5119-28. doi: 10.1021/jp302124v. Epub 2012 May 17.
The molecular structures of low-lying isomers of anionic and neutral sodium auride clusters have been studied computationally at the second-order Møller-Plesset perturbation theory level using quadruple-ζ basis sets augmented with a double set of polarization functions. The first vertical detachment energies were calculated at the Møller-Plesset level as the energy difference between the cluster anion and the corresponding neutral cluster. The photodetachment energies of higher-lying ionization channels were calculated by adding electronic excitation energies of the neutral clusters to the first vertical detachment energy. The excitation energies were calculated at the linear response approximate coupled-cluster singles and doubles level using the anionic cluster structures. The obtained ionization energies for NaAu(-), NaAu(2)(-), NaAu(3)(-), NaAu(4)(-), Na(2)Au(2)(-), Na(2)Au(3)(-), Na(3)Au(3)(-), and Na(2)Au(4)(-) were compared to values deduced from experimental photoelectron spectra. Comparison of the calculated photoelectron spectra for a few energetically low-lying isomers shows that the energetically lowest cluster structures obtained in the calculations do not always correspond to the clusters produced experimentally. Spin-component-scaled second-order Møller-Plesset perturbation theory calculations shift the order of the isomers such that the observed clusters more often correspond to the energetically lowest structure, whereas the spin-component-scaled approach does not improve the photodetachment energies of the sodium aurides. The potential energy surface of the sodium aurides is very soft, with several low-lying isomers requiring an accurate electron correlation treatment. The calculations show that merely the energetic criterion is not a reliable means to identify the structures of the observed sodium auride clusters; other experimental information is needed to ensure a correct assignment of the cluster structures. The cluster structures of nonstoichiometric anionic sodium aurides have been determined by comparing calculated ionization energies for low-lying structures of the anionic clusters with experimental data.
采用二阶 Møller-Plesset 微扰理论（MP2）水平的四元组-ζ基组，并用双极化函数对其进行了扩充，对阴离子和中性钠金化物团簇的低能异构物的分子结构进行了计算研究。第一垂直离解能是在 MP2 水平上通过计算阴离子团簇和相应的中性团簇之间的能量差来计算的。通过将中性团簇的电子激发能加到第一垂直离解能上，计算了较高电离通道的光离解能。用阴离子团簇结构，在线性响应近似耦合簇单双激发水平上计算了激发能。对于 NaAu(-)、NaAu(2)(-)、NaAu(3)(-)、NaAu(4)(-)、Na(2)Au(2)(-)、Na(2)Au(3)(-)、Na(3)Au(3)(-)和 Na(2)Au(4)(-)的获得的电离能与从实验光电子能谱推断的值进行了比较。对几个能量低的异构体的计算光电子能谱的比较表明，在计算中获得的能量最低的团簇结构并不总是与实验中产生的团簇相对应。自旋分量标度的二阶 Møller-Plesset 微扰理论（MP2）计算将异构体的顺序移动，使得观察到的团簇更经常对应于能量最低的结构，而自旋分量标度的方法并不能提高钠金化物的光离解能。钠金化物的势能表面非常柔软，有几个低能异构体需要精确的电子相关处理。计算表明，仅仅是能量标准并不是识别观察到的钠金化物团簇结构的可靠手段；需要其他实验信息来确保团簇结构的正确分配。通过比较低能阴离子团簇的计算电离能与实验数据，确定了非化学计量阴离子钠金化物的团簇结构。
