Boron clusters have been widely studied theoretically for their geometrical properties and electronic structure using a variety of methodologies. An important cluster of boron is the B$_{12}$ cluster whose two main isomers have distinct geometries, namely, icosahedral ($I_{h}$) and quasi planar ($C_{3v}$). In this paper we investigate the linear optical absorption spectrum of these two B$_{12}$ structures with the aim of examining the role of geometry on the optical properties of clusters. The optical absorption calculations are performed using both the semi-empirical and the ab initio approaches. The semi-empirical approach uses a wave function methodology employing the INDO model Hamiltonian, coupled with large-scale configuration interaction (CI) calculations, to account for the electron-correlation effects. The \emph{ab initio} calculations are performed within a time-dependent-density-functional-theory (TDDFT) methodology. The results for the two approaches are in very good qualitative agreement with each other. Quantitatively speaking, results agree with each other in the lower energy region, while in the higher energy region, features predicted by the TDDFT approach are red-shifted as compared to the INDO-CI results. Both the approaches predict that the optical absorption begins at much lower energies in the icosahedral cluster as compared to the planar one, a fact which can be utilized in experiments to distinguish between the two geometries. At higher energies, both the isomers exhibit plasmon-like excitations. 73,1 4%
Photo-absorption spectra of small hydrogenated silicon clusters using the time-dependent density functional theory
本文用含时密度泛函理论（TDDFT）研究了Si $_{n}$ H $_{m}$团簇（n=1-10，m=1-14）的光吸收谱.该方法使用的TDDFT涉及时间相关的Kohn-Sham方程的全传播的实时，实空间实现。我们对SiH $_{4}$和Si $_{2}$ H $_{6}$的计算结果与以前的计算和实验数据吻合得很好。我们发现，对于小团簇（n<7）的光吸收光谱是原子状的，而对于较大的团簇，它表现出块状的行为。我们研究了硅团簇的光吸收光谱作为氢化的函数。对于单氢化，我们发现，在一般情况下，吸收光学带隙减小，随着硅原子的数目增加，单个氢原子的光学带隙的影响减小。对于进一步氢化的光学带隙增加，并且对于完全氢化的团簇，光学带隙与相应的纯硅团簇相比更大。
Structure, stability and optical absorption spectra of small Ti$_n$C$_x$ clusters: a first-principles approach
碳化钛分子团被认为是在富碳的渐近巨支星（AGB）的星周包层（CSE）中形成的，但迄今为止，它们的探测仍然难以捉摸。为了便于在AGB和后AGB环境中对这些星系团进行天体物理识别，对小的Ti $_n$ C $_x$（n = 1-4，x = 1 -4）和一些选定的较大星系团Ti $_3$ C $_8$，Ti $_4$ C $_8$，Ti $_6$ C $_{13}$，Ti $_7$ C $_{13}$，Ti $_8$ C $_{12}$，计算了Ti $_9$ C $_{15}$和Ti $_{13}$ C $_{22}$。密度泛函的形式主义，在电子交换和相关的B3 LYP近似，被用来找到最低的能量结构。除了含有单个Ti原子的团簇外，其余的团簇均为三维结构。它们是由通常被碳二聚体包围的Ti碎片形成的。Ti $_n$ C $_x$的光谱，计算的含时密度泛函理论，使用修正的CAM-B3 LYP功能，显示在可见光和近红外区域的吸收功能，这可能有助于在空间中识别这些集群。此外，大多数星团都有相当大的电偶极矩，使得射电天文学观测可以探测到它们。
First-principles characterisation of spectroscopic and bonding properties of cationic bismuth carbide clusters
振动和电子吸收光谱计算的（含时）密度泛函理论水平的铋碳化物簇Bi $_{n}$ C $_{2n}$ $^+$（$3 \le n \le 9$）表明显着差异的类型取决于簇的几何形状的键合。这些集群的电子电荷密度的分析突出键合的趋势与光谱信息一致。合并后的数据表明，较大的集群（$n > 5$）可能是动力学不稳定的协议在气体聚集源实验中获得的集群质量分布。从我们的计算得到的不同的集群的光谱指纹还表明，识别特定的Bi $_{n}$ C $_{2n}$ $^+$异构体的红外和光学吸收光谱的基础上应该是可能的。
Systematic First Principles Configuration-Interaction Calculations of Linear Optical Absorption Spectra in Silicon Hydrides : Si$_2$H$_{2n}$ ($n = 1-3$)
我们已经进行了第一性原理电子相关计算采用大基组优化的几何形状，并计算线性光学吸收光谱的各种低的构象的硅的硅：Si $_{2}$ H $_{2n}$，$n=1,2,3$。在耦合团簇单双微扰三重态理论水平上优化了各种异构体的几何构型，采用大规模多参考单双构型相互作用（MRSDCI）方法计算了它们的激发态和吸收光谱，该方法在复杂水平上考虑了电子相关效应.我们的计算光谱是第一个为Si $_{2}$ H $_{2}$和Si $_{2}$ H $_{4}$构象，而对于Si $_{2}$ H $_{6}$，我们获得了良好的协议与实验测量，表明我们的计算方法是可靠的。我们计算的吸收光谱表现出很强的结构-性质的关系，这表明基于它们的光学吸收指纹识别各种构象的可能性。此外，我们还对所选的光学激发态进行了几何优化，使我们对它们的性质有了更深入的了解。
