Highest electron affinity as a predictor of cluster anion structures

Recent Progress in Low-Energy Electron Elastic-Collisions with Multi-Electron Atoms and Fullerene Molecules

We briefly review recent applications of the Regge pole analysis to low-energy 0.0 ≤ E ≤ 10.0 eV electron elastic collisions with large multi-electron atoms and fullerene molecules. We then conclude with a demonstration of the sensitivity of the Regge pole-calculated Ramsauer–Townsend minima and shape resonances to the electronic structure and dynamics of the Bk and Cf actinide atoms, and their first time ever use as novel and rigorous validation of the recent experimental observation that identified Cf as a transitional element in the actinide series (A. Müller, et al., Nat. Commun. 12, 948 (2021)).

Fullerene Negative Ions: Formation and Catalysis

We first explore negative-ion formation in fullerenes C₄₄ to C₁₃₆ through low-energy electron elastic scattering total cross sections calculations using our Regge-pole methodology. Then, the formed negative ions C₄₄ˉ to C₁₃₆ˉ are used to investigate the catalysis of water oxidation to peroxide and water synthesis from H₂ and O₂. The exploited fundamental mechanism underlying negative-ion catalysis involves hydrogen bond strength-weakening/breaking in the transition state. Density Functional Theory transition state calculations found C₆₀ˉ optimal for both water and peroxide synthesis, C₁₀₀ˉ increases the energy barrier the most, and C₁₃₆ˉ the most effective catalyst in both water synthesis and oxidation to H₂O₂.

A sixteen-valence-electron carbon-group 13 family with global penta-atomic planar tetracoordinate carbon: an ionic strategy

The design of planar tetracoordinate carbon (ptC) has always been a challenge due to its unique bonding mode that necessitates the perfect balance between the carbon center and surrounding ligands both electronically and mechanically. A unique type of 18-valence-electron (18ve) template, i.e., CAl42-, has been found to be very effective in designing various novel 18ve-species upon skeletal substitution. In this work, we showed that though ptC is not the global structure for the parent 16ve-CAl4, suitable skeletal substitution can allow for a series of global minimum ptC species. Theoretical calculations at the level of CCSD(T)/def2-QZVP//B3LYP/def2-QZVP for 35 carbon-group 13 systems with 16-ve, i.e., CXaYbZcKd (X, Y, Z, K = Al/Ga/In/Tl; 0 ≤ a, b, c, d ≤ 4, a + b + c + d = 4), showed that 9 systems (CAl3Tl, CGa3Tl, CGa2Tl2, CAl2GaTl, CAl2InTl, CGa2InTl, CAlGa2Tl, CGa2InTl and CAlGaInTl) possess global minimum ptC and 2 systems (CAl3In and CAl2Tl2) have quasi-GM ptC. Except for CAl3Tl and CAl3In, all the ptCs were predicted for the first time. All these stable ptC structures have the same skeleton and can be described as the same ionic sub-structure, i.e., [A-]B+. This study not only enriches 16ve-ptC, but also directly demonstrates that utilizing an ionic strategy, non-ptC CAl4 also can be used as a template to extend the ptC family.

Medium-sized [Formula: see text] (n = 14-20) clusters: a combined study of photoelectron spectroscopy and DFT calculations

Size-selected anionic silicon clusters, [Formula: see text] (n  =  14-20), have been investigated by photoelectron spectroscopy and density functional theory (DFT) calculations. Low-energy structures of the clusters are globally searched for by using a genetic algorithm based on DFT calculations. The electronic density of states and vertical detachment energies have been simulated by using ten DFT functionals and compared to the experimental results. We systematically evaluated the DFT functionals for the calculation of the energetics of silicon clusters. CCSD(T) single-point energies based on MP2 optimized geometries for selected isomers of [Formula: see text] are also used as benchmark for the energy sequence. The HSE06 functional with aug-cc-pVDZ basis set is found to show the best performance. Our global minimum search corroborates that most of the lowest-energy structures of [Formula: see text] (n  =  14-20) clusters can be derived from assembling tricapped trigonal prisms in various ways. For most sizes previous structures are confirmed, whereas for [Formula: see text] a new structure has been found.

Photoelectron spectra of copper oxide cluster anions from first principles methods

We present results and analyses for the photoelectron spectra of small copper oxide cluster anions (CuO^-, Cu O2- , Cu O3- , and Cu₂O^-). The spectra are computed using various techniques, including density functional theory (DFT) with semi-local, global hybrid, and optimally tuned range-separated hybrid functionals, as well as many-body perturbation theory within the GW approximation based on various DFT starting points. The results are compared with each other and with the available experimental data. We conclude that as in many metal-organic systems, self-interaction errors are a major issue that is mitigated by hybrid functionals. However, these need to be balanced against a strong role of non-dynamical correlation-especially in smaller, more symmetric systems-where errors are alleviated by semi-local functionals. The relative importance of the two phenomena, including practical ways of balancing the two constraints, is discussed in detail.

Doping the cage. Re@Au11Pt and Ta@Au11Hg, as novel 18-ve trimetallic superatoms displaying a doped icosahedral golden cage

Trimetallic superatomic clusters. Theoretical proposal and evaluation of the 18-ve Ta@Au₁₁Hg and Re@Au₁₁Pt clusters.

Chemical Interaction, Space-charge Layer and Molecule Charging Energy for a TiO2/TCNQ Interface

Three driving forces control the energy level alignment between transition-metal oxides and organic materials: the chemical interaction between the two materials, the organic electronegativity and the possible space charge layer formed in the oxide. This is illustrated in this study by analyzing experimentally and theoretically a paradigmatic case, the TiO₂(110) / TCNQ interface: due to the chemical interaction between the two materials, the organic electron affinity level is located below the Fermi energy of the n-doped TiO₂. Then, one electron is transferred from the oxide to this level and a space charge layer is developed in the oxide inducing an important increase in the interface dipole and in the oxide work-function.

Photoelectron velocity-map imaging spectroscopic and theoretical study on the reactivity of the gold atom toward CH3SH, CH3OH, and H2O

Photoelectron velocity-map imaging spectroscopy has been used to study the reaction of the anionic gold atom with the HR (R = SCH3, OCH3, OH) molecules. The solvated [Au···HR](-) and inserted [HAuR](-) products have been experimentally observed for R = SCH3, whereas only solvated [Au⋯HR](-) products were found for R = OCH3 and OH. This significant difference in the photoelectron spectra suggests the different reactivity of the Au(-) toward the CH3SH, CH3OH, and H2O molecules. Second order Møller-Plesset perturbation theory and coupled-cluster single double triple excitation calculations have been performed to aid the structural assignment of the spectra and to explore the reaction mechanism. Activation energies for the isomerizations of the solvated structures to the inserted ones in the Au(-)∕Au + HR reactions (R = OCH3 and OH) are predicted to be much higher than those for the Au(-)∕Au + CH3SH reactions, supporting the experimental observation. Theoretical calculations provide the evidence that the intriguing [HAuSCH3](-) product may be formed by the attachment of the electron onto the neutral HAuSCH3 species or the isomerization from the anionic [Au···HSCH3](-) one. These findings should be helpful for understanding the feature that the thiols are able to form the staple motifs, whereas CH3OH and H2O are not.

Structure selection based on high vertical electron affinity for TiO2 clusters

We study the structure and electronic properties of (TiO2)(2-10) clusters by using basin hopping based on density functional theory, combined with many-body perturbation theory. We show that in photoemission experiments performed on anions isomers with high electron affinity are selectively observed rather than those with the lowest energy. These isomers possess a highly reactive Ti3+ site. The selectivity for highly reactive clusters may be exploited for applications in catalysis.

Density functional investigations on structural and electronic properties of anionic and neutral sodium clusters Na(N) (N = 40-147): comparison with the experimental photoelectron spectra

Density functional calculations have been carried out to obtain low energy equilibrium geometries of anionic and neutral sodium clusters over a wide range of sizes 40 ≤ N ≤ 147, where N is the number of atoms. An exhaustive search for the low energy equilibrium geometries has been carried out. The density of states of the lowest energy geometries are compared with the experimental photoelectron spectra (Huber et al 2009 Phys. Rev. B 80 235425; Kostko et al 2007 Phys. Rev. Lett.98 043401) for N > 41. The agreement between theory and experiment is good for almost all the clusters and the changes in the spectrum with size correlate very well with the changes in the shapes as observed in the evolutionary trend of the ground state geometries.

Step by step towards understanding gold glyconanoparticles as elements of the nanoworld

Gold glyconanoparticles as elements of the nanoworld belong to a group of particles with diameters not exceeding 100 nm. This size scale makes them conformable to common biomolecules. A gold glyconanoparticle consists of three different parts: the gold core, the linkers, and saccharide ligands. The glycocalyx-like surface of these particles mimics the presentation of carbohydrate epitopes of cell surface glycoconjugates. As a consequence, gold glyconanoparticles provide inimitable tools for probing and manipulating the mechanisms of biological processes based on carbohydrate interactions. Each component of the gold glyconanoparticle has a profound effect on the nanoparticle’s properties. Therefore, in this review, elucidation of the overall behavior and properties of gold glyconanoparticles is based on a step by step (component by component) description of the system.

Density functional theory study of geometrical structures and electronic properties of silica nanowires

Silica nanowires are expected to possess structural diversity like bulk silica. We modeled three silica nanowires based on the side-shared two-membered rings, spiro-united two-membered rings, and three-membered rings, respectively. By performing density functional theory calculations, we studied their geometrical structures and electronic properties with and without the presence of external electric field. It is found that the stability of silica nanowires increases with length and diameter. As indicated by calculated large HOMO-LUMO gaps, silica nanowires are expected to be good insulating materials. The energy gaps, however, gradually decrease with applied electronic field and finally close, resulting in the breakdown of the insulating nanowires. Moreover, it is shown that the breakdown threshold remarkably increases with the nanowire diameter. These significant findings from the present calculations for the simplest silica nanowires will provide relevant insight into the structures and properties of much more complicated real silica nanowires.

A Synthetic Route toward Well-Defined Stoichiometric Silica Fullerene and Nanotubes Based on Metastable Four-Membered Rings

On the basis of computational considerations, using metastable four-membered rings as building blocks, we propose novel synthetic routes toward well-defined stoichiometric silica nanofullerenes and nanotubes. The viability of the routes has been demonstrated by performing high-level density functional calculations, and the so-formed nanoarchitectures were proved to be energetically and structurally stable. Such nanostructures, if synthesized, are expected to have potential application in nanotechnology.

Symmetry considerations in CdSe nanocrystals

Semiconductor nanocrystals or quantum dots show a wide range of physical properties depending on their size or shape. In this paper, we show that symmetry is also an important characteristic that can lead to different electronic and optical properties. We use pseudopotential density-functional theory, within a real space approach, and address the sensitivity of electronic and optical properties with respect to the symmetry point groups associated to CdSe nanocrystals.

Structural Model of Silica Nanowire Assembled from a Highly Stable (SiO2)8 Unit

The ground-state structures of silica clusters (SiO2)n for n = 1-8 were studied by performing calculations at the B3LYP/6-311+G(d) level of density functional theory. The results indicate that the growth mode of a silica nanowire based on small silica clusters may change at different wire lengths. A linear chain might be assembled from the smallest clusters of rhombic two-membered ring (2MR) with n < or = 5, while the growth motif changes at n = 6 into a more compact form composed of three-membered-rings (3MRs). The 3MR-containing structures become energetically favorable configurations for even longer silica clusters. In particular, the closed molecular ring consisting of 3MRs at n = 8 (i.e., (SiO2)8) with a high symmetry shows extreme energetic stability and relatively high chemical reactivity and thus is considered to be an important building block to assemble into silica nanowires. The relative stability of so-assembled silica nanowires were evaluated and compared with the models of silica nanowires in the literature.

Photoelectron spectroscopy as a structural probe of intermediate size clusters

We examine the utility of photoelectron spectroscopy (PES) as a structural probe of Si(n) (-) in the n=20-26 size range by determining isomers and associated photoelectron spectra from first principles calculations. Across the entire size range, we consistently obtain a good agreement between the theory and experiment [Hoffmann et al., Eur. Phys. J. D 16, 9 (2001)]. We find that PES can almost invariably distinguish between structurally distinct isomers at a given cluster size, but that structurally similar isomers usually cannot be reliably distinguished by PES. For many, but not all, sizes the isomer giving the best match to experiment is the lowest-energy one found theoretically. Thus, combining theory with PES experiments emerges as a useful source of structural information even for intermediate size clusters.

Geometric and Electronic Structures of Multiple-Decker One-End Open Sandwich Clusters: Eun(C8H8)n- (n = 1−4)

We have measured the photoelectron spectra of the multiple-decker 1:1 sandwich clusters of Eu(n)(COT)n- (n = 1-4; COT = 1,3,5,7-cyclooctatetraene), synthesized in the gas phase, and studied theoretically the bonding scheme, charge distribution, valence orbital energies, and photodetachment energies. We calculated the ground electronic state X- and the first excited electronic state A-, both of which have strong ionic bonding and a characteristic charge distribution. Moreover, we found that the valence orbital energies of Eu (6s) and COT (L delta) depend strongly on cluster size and their positions in the clusters. With the calculated vertical detachment energies for these valence orbitals, we assigned the peaks in the experimental photoelectron spectra and analyzed the origin of their interesting behavior by employing simple point charge models. From these analyses, it became clear that the characteristic behavior of the spectra is due to the strong ionic bonding and the charge distribution. In addition, using the point charge models, we estimated the vertical detachment energies of the one-dimensional polymer [Eu(COT)]infinity-.

Hydrocarbon analogues of boron clusters--planarity, aromaticity and antiaromaticity

An interesting feature of elemental boron and boron compounds is the occurrence of highly symmetric icosahedral clusters. The rich chemistry of boron is also dominated by three-dimensional cage structures. Despite its proximity to carbon in the periodic table, elemental boron clusters have been scarcely studied experimentally and their structures and chemical bonding have not been fully elucidated. Here we report experimental and theoretical evidence that small boron clusters prefer planar structures and exhibit aromaticity and antiaromaticity according to the Hückel rules, akin to planar hydrocarbons. Aromatic boron clusters possess more circular shapes whereas antiaromatic boron clusters are elongated, analogous to structural distortions of antiaromatic hydrocarbons. The planar boron clusters are thus the only series of molecules other than the hydrocarbons to exhibit size-dependent aromatic and antiaromatic behaviour and represent a new dimension of boron chemistry. The stable aromatic boron clusters may exhibit similar chemistries to that of benzene, such as forming sandwich-type metal compounds.