Center for Computational Physics, University of Coimbra, Rua Larga, 3004-516 Coimbra, Portugal.
J Chem Phys. 2009 Dec 7;131(21):214302. doi: 10.1063/1.3265767.
Upon ionization, rare-gas (like Ar and Xe) clusters shift their absorption spectrum from the ultraviolet to the visible. This happens as bonding becomes much stronger due to the removal of an electron from a strongly antibonding orbital. In this article, we study the absorption spectrum of small cationic xenon clusters (Xe(n) (+), with n=3,...,35) by means of time-dependent density functional theory. These calculations include relativistic effects through the use of relativistic j-dependent pseudopotentials in a two-spinor formulation of the Kohn-Sham equations. The peak positions in our calculated spectra are in fairly good agreement with experiment and confirm that absorption is mainly due to a charged linear core composed of 3, 4, or 5 Xe atoms where the positive charge is localized. However, we find large deviations concerning the oscillator strengths, which can be partially explained by the unsatisfactory treatment of exchange in common density functionals. Furthermore, we find that adequate ground-state geometries are necessary for the correct prediction of the qualitative features of the spectra.
稀有气体（如 Ar 和 Xe）团簇在电离后，其吸收光谱会从紫外区转移到可见区。这是因为电子从强反键轨道中被移除后，键合变得更强。在本文中，我们通过含时密度泛函理论研究了小的阳离子氙团簇（Xe(n) (+)，其中 n=3，...，35）的吸收光谱。这些计算通过在 Kohn-Sham 方程的双旋量形式中使用相对论 j 相关赝势来考虑相对论效应。我们计算出的光谱中峰的位置与实验相当吻合，证实了吸收主要是由于由 3、4 或 5 个 Xe 原子组成的带电荷的线性核心所致，其中正电荷被局域化。然而，我们发现振子强度存在较大偏差，这可以部分解释为常见密度泛函中交换的处理不当。此外，我们发现适当的基态几何形状对于正确预测光谱的定性特征是必要的。
