Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
J Chem Phys. 2010 Nov 7;133(17):174114. doi: 10.1063/1.3488230.
Standard implementations of time-dependent density-functional theory (TDDFT) for the calculation of excitation energies give access to a number of the lowest-lying electronic excitations of a molecule under study. For extended systems, this can become cumbersome if a particular excited state is sought-after because many electronic transitions may be present. This often means that even for systems of moderate size, a multitude of excited states needs to be calculated to cover a certain energy range. Here, we present an algorithm for the selective determination of predefined excited electronic states in an extended system. A guess transition density in terms of orbital transitions has to be provided for the excitation that shall be optimized. The approach employs root-homing techniques together with iterative subspace diagonalization methods to optimize the electronic transition. We illustrate the advantages of this method for solvated molecules, core-excitations of metal complexes, and adsorbates at cluster surfaces. In particular, we study the local π→π(∗) excitation of a pyridine molecule adsorbed at a silver cluster. It is shown that the method works very efficiently even for high-lying excited states. We demonstrate that the assumption of a single, well-defined local excitation is, in general, not justified for extended systems, which can lead to root-switching during optimization. In those cases, the method can give important information about the spectral distribution of the orbital transition employed as a guess.
基于含时密度泛函理论（TDDFT）的标准实现方法可用于计算研究分子的一系列最低电子激发能。对于扩展体系，如果需要寻找特定的激发态，这可能会变得很繁琐，因为可能存在许多电子跃迁。这通常意味着，即使对于中等大小的体系，也需要计算大量的激发态来覆盖特定的能量范围。在这里，我们提出了一种在扩展体系中选择性确定预定义激发电子态的算法。对于要优化的激发，需要提供关于轨道跃迁的猜测跃迁密度。该方法采用根归巢技术和迭代子空间对角化方法来优化电子跃迁。我们举例说明了该方法在溶剂化分子、金属配合物的芯激发和团簇表面吸附物中的优势。特别是，我们研究了吸附在银团簇上的吡啶分子的局部π→π*(∗)激发。结果表明，即使对于高能激发态，该方法也能非常有效地工作。我们证明，对于扩展体系，假设单个明确的局部激发通常是不合理的，这可能导致在优化过程中出现根切换。在这些情况下，该方法可以提供有关用作猜测的轨道跃迁的光谱分布的重要信息。
