Structures of Small Tantalum Cluster Anions: Experiment and Theory.

We present a study of the structural evolution of tantalum cluster anions Ta, 6 ≤ ≤ 13 using a combination of trapped ion electron diffraction (TIED) experiments with a variety of electronic structure methods. A genetic algorithm has been employed to establish a set of likely structures for each cluster, their geometries and energetics have been studied by density functional theory (DFT), random phase approximation, and two-component (2C) DFT methods, which include spin-orbit coupling. We find octahedral structures for Ta and Ta as well as structures based on the pentagonal bipyramid (Ta and Ta). Ta-Ta are defective icosahedral structures and Ta is a distorted icosahedron. For most clusters, we find a good agreement between the theoretically predicted ground-state structures, especially those determined by the 2C method and the TIED results.