Elucidation of the molecular and electronic structures of some magic silver clusters Ag n (n = 8, 18, 20 (original) (raw)
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Physical Review A, 2003
The formalism of second-order many-body perturbation theory has been applied to investigate the electronic and geometric structures of neutral, cationic, and anionic Ag n (nϭ5 -9) clusters. Hay-Wadt relativistic effective core potentials replacing the 28 core electrons and a Gaussian basis set have been used. Full geometry optimizations of topologically different clusters and clusters belonging to different symmetry groups have been carried out. The neutral silver clusters prefer planar geometry up to nϭ6 and the charged clusters prefer three-dimensional geometry from nϭ6. Binding energies, ionization potentials, electron affinities, and fragmentation energies of the optimized clusters have been compared with other experimental and theoretical results available in the literature. Based on different criteria, we predict the eight-atom silver cluster to be a magic-number cluster.
A Correlation Study of Small Silver Clusters
The European Physical Journal D, 2003
The formalisms of many body perturbation theory and coupled cluster theory have been used to study the electronic and geometric structures of neutral, cationic, and anionic small silver clusters. Hay-Wadt relativistic effective core potentials replacing the twenty-eight core electrons and a Gaussian basis set have been used. Topologically different clusters and clusters belonging to different symmetry groups have been identified and studied in detail. Full geometry optimizations have been carried out at four different correlated levels of theories. Ionization potentials, electron affinities, and fragmentation energies of the optimized clusters have been compared with other experimental and theoretical results available in the literature. No convergence problems are encountered at the various levels of correlated theories. This is noteworthy since it has been claimed in the literature that for d elements the MP series does not converge very well.
2020
Our article is a systematic study toward understanding the mechanism of silver cluster formation. We calculated optical spectra of ultra-small silver clusters using time-dependent density functional theory (TDDFT) and compared our results with time-resolved UV-Vis spectra obtained from pulse radiolysis experiments during early stages of cluster formation. This comparative study indicates that the formation mechanism of silver clusters occurs through both monomer and ion addition growth pathways. Also, we calculated free energy of formation of small cationic and neutral clusters using density functional theory (DFT) which shows the thermodynamic stability of cationic clusters. In a conventional experimental system with the common reducing agents, the formation of cationic clusters is kinetically favored owing to the dominance of charged ions relative to neutral atoms in the system. While we show the stability of small cationic clusters relative to neutral clusters, collectively, we d...
Journal of Physical Chemistry A, 2007
Low-lying equilibrium geometric structures of Al n N (n ϭ 1-12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spinpolarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee-Yang-Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static dipole polarizabilities are calculated for the ground-state structures within the GGA. It is observed that symmetric structures with the nitrogen atom occupying the internal position are lowest-energy geometries. Generalized gradient approximation extends bond lengths as compared with the LSDA lengths. The odd-even oscillations in the dissociation energy, the second differences in energy, the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within the GGA. The stability analysis based on the energies clearly shows the Al 7 N cluster to be endowed with special stability.
Nanoscale Molecular Silver Cluster Compounds in Gram Quantities
Angewandte Chemie International Edition, 2014
Dedicated to Professor Bernt Krebs on the occasion of his 75th birthday cluster compounds · gold · nanoparticles · silver · silver sulfide Fundamental knowledge of the intermediates between bulk materials (ionic, metallic) and molecular entities (e.g. clusters) is essential for the development of nanotechnology. The following interrelation exists between these areas, where the average oxidation number n of the metal atoms is a significant measure for the different metal-atom cluster types: "naked" metal-atom clusters (n = 0) stabilized with neutral ligands (PR 3 ), metalloid cluster compounds (0 n av n salt ) exhibiting even conductivity and superconductivity behavior, and saltlike cluster compounds which are mostly semi-conducting). The nanoscience of crystalline cluster compounds connect classical inorganic chemistry (bulk metals/bulk salts) with modern inorganic physical chemistry and physics.
Density functional investigation of silver, palladium and silver-palladium small sized clusters
2009
En este trabajo presentamos los resultados del estudio de la propiedades estructurales y electronicas de cumulos pequenos de Ag y Pd asi como cumulo bimetalicos Ag-Pd. Haciendo uso de pseudopotenciales en un esquema basado en teoria de los funcionales de la densidad electronica, determinamos las propiedades geometricas la multiplicidad de espin del estado fundamental para estos sistemas. Calculamos la energias de cohesion y la energia de adicion de atomos para estas familias de cumulos haciendo uso de dos distintos funcionales de la densidad. Las dos series de cumulos de Ag y Pd muestran claramente comportamientos distintos. En particular, discutimos los resultados de cumulos de alta simetria y las tendencias en los cumulos bimetalicos Ag-Pd
Quantum Theoretical Study of Palladium and Silver Clusters
n and Ag n clusters (n = 2 thru 12). Transition-metal clusters can be useful for the study of quantum size effects and for formation of metallic states, and are ideal candidates for catalytic processes. Hybrid ab initio methods of quantum chemistry (particularly the DFT-B3LYP model) are used to derive optimal geometries for the clusters of interest. We compare calculated binding energies, bond-lengths, ionization potentials, electron affinities and HOMO-LUMO gaps for the clusters of the two different metals. Of particular interest are the comparisons of binding strengths at the three important types of sites: edge (E) sites, hollow sites (H) site and on-top (T) sites. Effects of crystal symmetries corresponding to the bulk structures for the two metals will also be investigated. The implications for the molecular dissociation of the H 2 and O 2 species will be considered.
Computational and Theoretical Chemistry, 2014
Density functional calculations using Wu and Cohen generalized gradient approximation functional are performed to investigate the structural properties and relative stability of silver doped gold clusters AgAu nÀ1 (n = 3-13). Low-lying energy structures include two dimensional and three dimensional geometries. Especially, for the lowest energy structures, the transition from planar to three dimensional structures is found to occur at n = 13 and the impurity Ag atom prefers to occupy higher coordination sites. The calculated binding energies, second-order differences in energies, dissociation energies and HOMO-LUMO energy gaps show pronounced odd-even oscillating behaviors, indicating that clusters with even number of atoms keep a higher relative stability than their neighboring odd-numbered ones. Particularly, the cluster AgAu 5 shows the strongest stability. Moreover, vertical ionization potential, vertical electronic affinity, and chemical hardness are discussed and compared in depth. The same odd-even oscillations are found.
Density functional theory and surface reactivity study of bimetallic Ag n Y m (n+m = 10) clusters
Solid State Sciences, 2018
Density functional theory calculations have been performed on pure silver (Ag n), yttrium (Y m) and bimetallic silver yttrium clusters Ag n Y m (n+m = 2-10) for reactivity descriptors in order to realize sites for nucleophilic and electrophilic attack. The reactivity descriptors of the clusters, studied as a function of cluster size and shape, reveal the presence of different type of reactive sites in a cluster. The size and shape of the pure silver, yttrium and bimetallic silver yttrium cluster (n = 2-10) strongly influences the number and position of active sites for an electrophilic and/or nucleophilic attack. The trends of reactivities through reactivity descriptors are confirmed through comparison with experimental data for CO binding with silver clusters. Moreover, the adsorption of CO on bimetallic silver yttrium clusters is also evaluated. The trends of binding energies support the reactivity descriptors values. Doping of pure cluster with the other element also influence the hardness, softness and chemical reactivity of the clusters. The softness increases as we increase the number of silver atoms in the cluster, whereas the hardness decreases. The chemical reactivity increases with silver doping whereas it decreases by increasing yttrium concentration. Silver atoms are nucleophilic in small clusters but changed to electrophilic in large clusters.
Molecular-dynamics simulations of silver clusters
Physica E: Low-dimensional Systems and Nanostructures, 1999
Structural stability and energetics of silver clusters, Agn (n = 3-177), have been investigated by molecular-dynamics simulations. An empirical model potential energy function has been used in the simulations. Stable structures of the microclusters with sizes n = 3-13 and clusters generated from FCC crystal structure with sizes n = 13-177 have been determined by molecular-dynamics simulation. Five-fold symmetry appears on the spherical clusters.