Chemisorptions effect of oxygen on the geometries, electronic and magnetic properties of small size Nin (n = 1-6) clusters

Exploring structures of small anionic nickel-ethanol clusters with infrared spectroscopy

Small anionic nickel clusters with ethanol are investigated with a combination of mass-selective infrared photodissociation spectroscopy in a molecular beam and density functional theory simulations at the BLYP/6-311g(d,p) and TPSSh/def2-TZVPP level. In this context, the O-H stretching vibration of the ethanol is analyzed to obtain information about the structural motif, the geometry of the metal core, and the spin state of the clusters. For the [Ni2(EtOH)]- and [Ni3(EtOH)]- clusters, we assign quartet states of motifs with a hydrogen bond from the ethanol to the linear nickel core. The aggregation of a further ethanol molecule, yielding the [Ni3(EtOH)2]- cluster, results in the formation of a cooperative hydrogen bond network between the nickel core and the two ethanol molecules.

Orbital-Dependent Photodynamics of Strongly Correlated Nickel Oxide Clusters

The ultrafast electronic relaxation dynamics of neutral nickel oxide clusters were investigated with femtosecond pump-probe spectroscopy and supported with theoretical calculations to reveal that their excited state lifetimes are strongly...

Recyclabl Metal (Ni, Fe) Cluster Designed Catalyst for Cellulose Pyrolysis to Upgrade Bio-Oil

A new recyclable catalyst for pyrolysis has been developed by combining calculations and experimental methods. In order to understand the properties of the new cluster designed catalysts, cellulose (a major component of plants) as a biomass model compound was pyrolyzed and catalyzed with different cluster designed catalysts. The NiaFeb (2 ≤ a + b ≤ 6) catalyst clusters structures were calculated by using Gaussian and Materials Studio software to determine the relationships between catalyst structure and bio-oil components, which is essential to design cluster designed catalysts that can improve bio-oil quality. GC-MS analysis of the bio-oil was used to measure the effects on the different catalyst interactions with cellulose. It was found that the NiFe cluster designed catalysts can increase the yield of bio-oil from 35.8% ± 0.9% to 41.1% ± 0.6% and change the bio-oil composition without substantially increasing the water content, while substantially decreasing the sugar concentration from 40.1% ± 1.3% to 27.5% ± 0.9% and also producing a small amount of hydrocarbon compounds. The catalyst with a high Ni ratio also had high Gibbs free energy, ΔG, likely also influencing the decrease of sugar and acid while increasing the ketone concentrations. These results indicate the theoretical calculations can enhance the design next-generation cluster designed catalysts to improve bio-oil composition based upon experiments.

Computational Approach To Reveal the Structural Stability and Electronic Properties of Lithiated M/CNT (M = Si, Ge) Nanocomposites as Anodes for Lithium-Ion Batteries

This work is motivated to explore the structural stability and electronic and electrochemical properties of nanocomposites of M₄Li _n (M = Si and Ge)-carbon nanotube (CNT) by employing first-principles density functional theory calculations. By analyzing the structural stability of various M₄Li _n (n = 0-10) clusters, it is revealed that a tetrahedron-shaped M₄Li₄ Zintl cluster is found to be highly stable. Our study on the interaction between the lithiated clusters and CNT illustrates that the charge transfer from the former to latter plays a pivotal role in stabilizing these nanocomposites. The structural stability of those nanocomposites arises as a consequence of bonding between lithiated clusters and CNT, which is mediated through the cation-π interaction. The strength of the interaction between them is well reflected in electronic structure calculations by shifting the energy levels with respect to the Fermi energy. Further, the electrochemical properties of these nanocomposites are explored by forming an assembly of the cluster-inserted CNT. The calculated average intercalation voltage of the systems is found to be low (maximum ∼1.0 V for M = Si and 1.05 V for M = Ge), which demonstrates their anodic behavior.

Magnetic properties of oxygen doped samarium clusters

Here we present the results of experimental study of magnetic properties of samarium clusters doped with a single oxygen atom. In a recent theoretical study it was observed that for pure Sm clusters a transition from fully non-magnetic to weakly magnetic occurs due to a valence change occurring at a size of eight atoms. Here we found, first, that pure Sm clusters could not be synthesized due to the strong oxidation tendency of Sm and the inability to sufficiently remove oxygen from the setup. Therefore, we studied Sm[Formula: see text]O clusters. Since the oxygen contributes to the binding, the valence transition for Sm[Formula: see text]O clusters may be expected to occur for a smaller cluster size than for pure Sm clusters. Indeed from our experiments the valence transition is indicated to occur for [Formula: see text] Sm atoms instead of [Formula: see text]. Furthermore, the observed magnetic moment as function of cluster size for Sm[Formula: see text]O clusters shows a strong dependency of the magnetic moment on the cluster size. A large total magnetic moment is observed for Sm[Formula: see text]O, Sm[Formula: see text]O, Sm[Formula: see text]O and Sm[Formula: see text]O compared to the smaller moment for Sm[Formula: see text]O to Sm[Formula: see text]O and Sm[Formula: see text]O to Sm[Formula: see text]O.

Uniaxial magnetic anisotropy energy of bimetallic Co-Ni clusters from a first-principles perspective

Along with the growing precision in the control of matter at increasingly smaller size scales, a field of research, based onto magnetic materials of technical interest, such as bimetallic clusters, has been developed in very recent years. Thereby, here, we report on a complete study of bimetallic clusters composed of cobalt and nickel with up to 7 atoms using ab initio methods in the GGA approach. We applied an unrestricted search method based on the tensor of inertia eigenvalues to find the most stable configurations of the clusters, obtaining a diverse set of structures with different geometric properties. We explored the effect of composition on the structural properties, the chemical stability, the magnetization and the magnetic anisotropy energy (MAE) of the so-obtained systems. Our results indicate that the behavior of the clusters is mainly governed by the Co-Co interaction and to a lesser extent by the Co-Ni and Ni-Ni interactions. Furthermore, for a given cluster size the magnetic moment increases by 2 μB/Co-substitution plus 1 μB/Ni-substitution coming from the cobalt and nickel core d-states, while in some cases unpaired hybrid s-electrons can also give rise to itinerant magnetism. These features have been analyzed with the help of a Jellium model and have important consequences for the magnetism and the magnetic anisotropy of the clusters. The magnetic behavior and MAE present complex and intriguing landscapes, which suggests the possibility of finely controlling the magnetic states, by tuning the cluster composition, aiming at technical implementation in fields such as molecular magnetism or quantum computation. In particular, cases such as Co6Ni, Co4Ni3, CoNi6 Co2Ni5 and Co3Ni3 present high relative stability and enhanced magnetic moments (around 10 μB), what makes them promising candidates for applications such as subnanometer magnetic information storage.

Sequential oxygen chemisorption on Fe13 clusters: from first-principles to practical insights

With the advent of more precise technologies allowing manipulation of matter at nanoscopic scales and novel characterization techniques, a growing field of research is focused on magnetic materials of technical interest-such as Fe clusters-and their related physical-chemical processes. In this study, we present the results of the sequential oxidation process of the Fe₁₃ cluster by considering the physical-chemistry properties of the ground state configurations of Fe₁₃O _n ([Formula: see text]) clusters. We develop an exhaustive ab initio study into the GGA approach and explore the effect of the chemisorption of oxygen on the structural properties, the chemical stability, the magnetization and the magnetic anisotropy energy (MAE) of the systems. Our results clearly indicate that: (i) one of the studied clusters, Fe₁₃O₁₇, presents the biggest electrophilicity index and the lowest chemical hardness, being the most reactive among the systems studied; (ii) the Fe₁₃O₁₀ exhibits a much more enhanced magnetization than other related clusters intended for health and technology applications (Sun et al 2007 J. Phys. Chem. C 111 4159-63), so that it might be a better candidate for those purposes; and (iii) the MAE presents a complex and intriguing landscape that encourages thinking about the plausible control of magnetic states focused on technical applications.

Study of electronic properties, stabilities and magnetic quenching of molybdenum-doped germanium clusters: a density functional investigation

The evolution of electronic structures, properties and stabilities of neutral and cationic molybdenum encapsulated germanium clusters (Mo@Ge_n, n = 1 to 20) has been investigated.