skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Interplay of electronic and geometry shell effects in properties of neutral and charged Sr clusters

Abstract

The optimized structure and electronic properties of neutral, singly, and doubly charged strontium clusters have been investigated using ab initio theoretical methods based on density-functional theory. We have systematically calculated the optimized geometries of neutral, singly, and doubly charged strontium clusters consisting of up to 14 atoms, average bonding distances, electronic shell closures, binding energies per atom, the gap between the highest occupied and the lowest unoccupied molecular orbitals, and spectra of the density of electronic states (DOS). It is demonstrated that the size evolution of structural and electronic properties of strontium clusters is governed by an interplay of the electronic and geometry shell closures. Influence of the electronic shell effects on structural rearrangements can lead to violation of the icosahedral growth motif of strontium clusters. It is shown that the excessive charge essentially affects the optimized geometry of strontium clusters. Ionization of small strontium clusters results in the alteration of the magic numbers. The strong dependence of the DOS spectra on details of ionic structure allows one to perform a reliable geometry identification of strontium clusters.

Authors:
 [1];  [2]; ; ;  [1]
  1. Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-University, Max-von-Laue Str. 1, 60438 Frankfurt am Main (Germany)
  2. (United Kingdom)
Publication Date:
OSTI Identifier:
20982542
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 75; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevA.75.053201; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ATOMIC CLUSTERS; ATOMS; BINDING ENERGY; DENSITY; DENSITY FUNCTIONAL METHOD; IONIZATION; MAGIC NUCLEI; SPECTRA; STRONTIUM

Citation Formats

Lyalin, Andrey, Imperial College of London, The Blackett Laboratory, Prince Consort Road, London SW7 2BW, Solov'yov, Ilia A., Solov'yov, Andrey V., and Greiner, Walter. Interplay of electronic and geometry shell effects in properties of neutral and charged Sr clusters. United States: N. p., 2007. Web. doi:10.1103/PHYSREVA.75.053201.
Lyalin, Andrey, Imperial College of London, The Blackett Laboratory, Prince Consort Road, London SW7 2BW, Solov'yov, Ilia A., Solov'yov, Andrey V., & Greiner, Walter. Interplay of electronic and geometry shell effects in properties of neutral and charged Sr clusters. United States. doi:10.1103/PHYSREVA.75.053201.
Lyalin, Andrey, Imperial College of London, The Blackett Laboratory, Prince Consort Road, London SW7 2BW, Solov'yov, Ilia A., Solov'yov, Andrey V., and Greiner, Walter. Tue . "Interplay of electronic and geometry shell effects in properties of neutral and charged Sr clusters". United States. doi:10.1103/PHYSREVA.75.053201.
@article{osti_20982542,
title = {Interplay of electronic and geometry shell effects in properties of neutral and charged Sr clusters},
author = {Lyalin, Andrey and Imperial College of London, The Blackett Laboratory, Prince Consort Road, London SW7 2BW and Solov'yov, Ilia A. and Solov'yov, Andrey V. and Greiner, Walter},
abstractNote = {The optimized structure and electronic properties of neutral, singly, and doubly charged strontium clusters have been investigated using ab initio theoretical methods based on density-functional theory. We have systematically calculated the optimized geometries of neutral, singly, and doubly charged strontium clusters consisting of up to 14 atoms, average bonding distances, electronic shell closures, binding energies per atom, the gap between the highest occupied and the lowest unoccupied molecular orbitals, and spectra of the density of electronic states (DOS). It is demonstrated that the size evolution of structural and electronic properties of strontium clusters is governed by an interplay of the electronic and geometry shell closures. Influence of the electronic shell effects on structural rearrangements can lead to violation of the icosahedral growth motif of strontium clusters. It is shown that the excessive charge essentially affects the optimized geometry of strontium clusters. Ionization of small strontium clusters results in the alteration of the magic numbers. The strong dependence of the DOS spectra on details of ionic structure allows one to perform a reliable geometry identification of strontium clusters.},
doi = {10.1103/PHYSREVA.75.053201},
journal = {Physical Review. A},
number = 5,
volume = 75,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the global equilibrium geometries and electronic structure of neutral, cationic, and anionic aluminum clusters containing up to 15 atoms. The total energies of these clusters are then used to study the evolution of their binding energy, relative stability, fragmentation channels, ionization potential, and vertical and adiabatic electron affinities as a function of size. The geometries are found to undergo a structural change from two dimensional to three dimensional when the cluster contains 6 atoms. An interior atom emerges only when clusters contain 11 or moremore » atoms. The geometrical changes are accompanied by corresponding changes in the coordination number and the electronic structure. The latter is reflected in the relative concentration of the {ital s} and {ital p} electrons of the highest occupied molecular orbital. Aluminum behaves as a monovalent atom in clusters containing less than seven atoms and as a trivalent atom in clusters containing seven or more atoms. The binding energy evolves monotonically with size, but Al{sub 7}, Al{sub 7}{sup +}, Al{sub 7}{sup {minus}}, Al{sub 11}{sup {minus}}, and Al{sub 13}{sup {minus}} exhibit greater stability than their neighbors. Although the neutral clusters do not conform to the jellium model, the enhanced stability of these charged clusters is demonstrated to be due to the electronic shell closure. The fragmentation proceeds preferably by the ejection of a single atom irrespective of the charge state of the parent clusters. While odd-atom clusters carry a magnetic moment of 1{mu}{sub B} as expected, clusters containing even number of atoms carry 2{mu}{sub B} for n{le}10 and 0&hthinsp;{mu}{sub B} for n{gt}10. The calculated results agree very well with all available experimental data on magnetic properties, ionization potentials, electron affinities, and fragmentation channels. The existence of isomers of Al{sub 13} cluster provides a unique perspective on the anomaly in the intensity distribution of the mass spectra. The unusual stability of Al{sub 7} in neutral, cationic, and anionic form compared to its neighboring clusters is argued to be due to its likely existence in a mixed-valence state. {copyright} {ital 1999 American Institute of Physics.}« less
  • The electronic and structural properties of neutral and charged Si{sub n}O{sub n} clusters, with n=3, 4, and 5, and related clusters, are examined using the higher-order finite-difference pseudopotential method. The ground-state structures for these clusters are determined via a simulated annealing procedure. The photoemission spectra for negatively charged clusters Si{sub n}O{sub n}{sup {minus}} are simulated at finite temperatures using quantum forces coupled with Langevin dynamics. The simulated spectra are in good agreement with measured spectra. In contrast to previously predicted structures, we find the lowest-energy structures for Si{sub 4}O{sub 4} and Si{sub 5}O{sub 5} correspond to nonplanar rings. {copyright} {italmore » 1998} {ital The American Physical Society}« less
  • Small metal clusters exhibit unique size and morphology dependent catalytic activity. The search for alternate minimum energy pathways and catalysts to transform methane to more useful chemicals and carbon nanomaterials led us to investigate collision induced dissociation of methane on small Cu clusters. We report here for the first time, the free energy barriers for the collision induced activation, dissociation, and coupling of methane on small Cu clusters (Cu{sub n} where n = 2–12) using ab initio molecular dynamics and metadynamics simulations. The collision induced activation of the stretching and bending vibrations of methane significantly reduces the free energy barriermore » for its dissociation. Increase in the cluster size reduces the barrier for dissociation of methane due to the corresponding increase in delocalisation of electron density within the cluster, as demonstrated using the electron localisation function topology analysis. This enables higher probability of favourable alignment of the C–H stretching vibration of methane towards regions of high electron density within the cluster and makes higher number of sites available for the chemisorption of CH{sub 3} and H upon dissociation. These characteristics contribute in lowering the barrier for dissociation of methane. Distortion and reorganisation of cluster geometry due to high temperature collision dynamics disturb electron delocalisation within them and increase the barrier for dissociation. Coupling reactions of CH{sub x} (x = 1–3) species and recombination of H with CH{sub x} have free energy barriers significantly lower than complete dehydrogenation of methane to carbon. Thus, competition favours the former reactions at high hydrogen saturation on the clusters.« less
  • A comparative analysis of bond lengths vertical detachment energies (VDE), excitation energies of neutral clusters with geometry of anions and vertical ionization potentials of neutral clusters calculated within density functional theory (DFT) using different functionals with both effective core potential (ECP) and all-electron basis sets for silver clusters Ag n, have been carried out. DFT methods provide a good agreement between calculated and experimental data of some characteristics. The accurate prediction of all characteristics simultaneously can be achieved with all-electron DZVP basis set only. A new functional has been developed. It provides results close to experimental data using the moderatemore » basis set. For anionic clusters Ag2?10-, the difference between calculations with this functional and experimental values of VDE and for the most stable isomers does not exceed 0.1 eV. Based on both total energy calculations and comparison of experimental and calculated photoelectron spectra, the structural assignment of clusters Ag7-, Ag9- and Ag10- has been made. The electronic structure and geometrical characteristics of the low-lying isomers has been studied.« less
  • {ital Ab initio} molecular orbital theory based on both density functional formalism and quantum chemical methods has been used to calculate the equilibrium geometries, binding energies, ionization potentials, fragmentation patterns, and electronic structures of neutral and charged boron clusters containing up to six atoms. Calculations have also been performed on restricted geometries for B{sub n}X (n=1,5,12; X=Be, B, C) and B{sub 20} clusters to see if clusters can be designed so as to increase their stability. Energetics of doubly charged B{sub n}{sup ++} clusters have also been studied to find the critical size for Coulomb explosion. The results are comparedmore » with existing experimental and theoretical data.{copyright} {ital 1997 American Institute of Physics.}« less