We report on the ab initio discovery of a novel putative ground state for quasi two-dimensional TiO2 through a structural search using the minima hopping method with an artificial neural network potential. The structure is based on a honeycomb lattice and is energetically lower than the experimentally reported lepidocrocite sheet by 7 meV/atom, and merely 13 meV/atom higher in energy than the ground state rutile bulk structure. According to our calculations, the hexagonal sheet is stable against mechanical stress, it is chemically inert and can be deposited on various substrates without disrupting the structure. Its properties differ significantly from all known TiO2 bulk phases with a large gap of 5.05 eV that can be tuned through strain engineering. arXiv:1704.03983v1 [cond-mat.mtrl-sci]

IR spectra of cationic copper clusters Cu n + ( n = 4–7) complexed with hydrogen molecules are recorded via IR multiple-photon dissociation (IRMPD) spectroscopy. To this end, the copper clusters are generated via laser ablation and reacted with H 2 and D 2 in a flow-tube-type reaction channel. The complexes formed are irradiated using IR light provided by the free-electron laser for intracavity experiments (FELICE). The spectra are interpreted by making use of isotope-induced shifts of the vibrational bands and by comparing them to density functional theory calculated spectra for candidate structures. The structural candidates have been obtained from global sampling with the minima hopping method, and spectra are calculated at the semilocal (PBE) and hybrid (PBE0) functional level. The highest-quality spectra have been recorded for [5Cu, 2H/2D] + , and we find that the semilocal functional provides better agreement for the lowest-energy isomers. The interaction of hydrogen with the copper clusters strongly depends on their size. Binding energies are largest for Cu 5 + , which goes hand in hand with the observed predominantly dissociative adsorption. Due to smaller binding energies for dissociated H 2 and D 2 for Cu 4 + , also a significant amount of molecular adsorption is observed as to be expected according to the Evans–Polanyi principle. This is confirmed by transition-state calculations for Cu 4 + and Cu 5 + , which show that hydrogen dissociation is not hindered by an endothermic reaction barrier for Cu 5 + and by a slightly endothermic barrier for Cu 4 + . For Cu 6 + and Cu 7 + , it was difficult to draw clear conclusions because the IR spectra could not be unambiguously assigned to structures.

We report on an extensive study of ZnO materials with cage-like motives in clusters and bulk phases through structural searches using the minima hopping method. A novel putative ground state was discovered for the (ZnO)32 cluster with a tube-like structure, closely related to the previously reported (ZnO)24 ground state cage geometry. Furthermore, the effect of ionization on the geometries and energetic ordering of (ZnO)n clusters with n = 3 − 10, 12 was studied by directly sampling the energy landscape of the ionized system. Our results indicate that the transition from ring and planar structures to 3D cages occurs at larger cluster sizes than in the neutral system. Inspired by the bottom-up design philosophy and the predominance of cage-like structures in medium-sized clusters, a search for crystalline ZnO was conducted aimed specifically at low density polymorphs, resulting in the discovery of 57 novel metastable phases. The voids in these low-density materials closely resemble the hollow cage structures of small (ZnO)n/(ZnO) + n clusters with n < 16. In analogy to clathrate materials, these voids could serve to accommodate guest atoms to tailor the materials properties for various applications.

To understand elementary reaction steps in the hydrogenation of CO2 over copper-based catalysts, we experimentally study the adsorption of CO2 and H2 onto cationic Cun+ (n = 4–7) clusters.

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