9 results on '"Springborg M"'
Search Results
2. Does the Boson Peaks Exist in Small Neutral Gold Clusters?
- Author
-
Springborg M and Vishwanathan K
- Subjects
Condensed Matter::Quantum Gases ,Range (particle radiation) ,Chemistry ,02 engineering and technology ,Low frequency ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Spectral line ,0104 chemical sciences ,Intensity (physics) ,Nuclear magnetic resonance ,Amplitude ,Far infrared ,Atom ,Atomic physics ,0210 nano-technology ,Boson - Abstract
The Boson peaks are typically ascribed to an excess density of vibrational states for the small clusters. A well resolved boson peak is observed in the low-frequency portion of the spectrum. A starting point for our discussion is the behaviour of the boson peak, derived from the vibrational density of states and the temperature dependencies of the vibrational heat capacities of the re-optimized neutral gold clusters. This Boson peak is associated with the existence of intermediate range order (IRO) in the arrangements of atoms. The low frequency (Far Infrared FIR, IR-C 200-10 cm−1) containing this dominant spectral line (Boson peak) is interpreted in terms of its relationship to the amplitude and extent of the density fluctuations in atoms and is, thereby, considered a measure of the intermediate range order in these atoms. We found a systematic relation among the boson peak energy, the boson peak intensity per atom, and the zigzag-bond density; the peak energy decreases and the peak intensity increases as zigzag-bond density decreases. more...
- Published
- 2017
- Full Text
- View/download PDF
Catalog
3. Symmetry of Gold Neutral Clusters Au3-20 and Normal Modes of Vibrations by using the Numerical Finite Difference Method with Density-Functional Tight-Binding(DFTB) Approach
- Author
-
Springborg M and Vishwanathan K
- Subjects
Hessian matrix ,Physics ,symbols.namesake ,Tight binding ,Normal mode ,Molecular vibration ,symbols ,Finite difference method ,Wavenumber ,Positive-definite matrix ,Microbiology ,Molecular physics ,Symmetry (physics) - Abstract
The geometries and vibrational frequency of the most stable small AuN clusters with N = 3 to 20 are presented through global structure re-optimization Study. The finite-differentiation method has been implemented within the density-functional tight-binding (DFTB) approach. The desired set of system eigenfrequencies (3N-6) is obtained by a diagonalization of the symmetric positive semi definite Hessian matrix. We have observed the vibrational modes between 0.55 and 370.72 cm-1 in wavenumbers at T=0 for the small gold clusters. The effect of the range of interatomic forces was calculated, and even the very lower frequencies were occupied in some clusters. more...
- Published
- 2017
- Full Text
- View/download PDF
4. Effect of Size, Temperature, and Structure on the Vibrational Heat Capacity of Small Neutral Gold Clusters
- Author
-
Springborg M and Vishwanathan K
- Subjects
Gold cluster ,Materials science ,010304 chemical physics ,media_common.quotation_subject ,Nanoparticle ,010402 general chemistry ,01 natural sciences ,Heat capacity ,Molecular physics ,Asymmetry ,0104 chemical sciences ,Molecular vibration ,0103 physical sciences ,Cluster (physics) ,Organic chemistry ,Particle size ,media_common ,Boson - Abstract
The vibrational heat capacity Cvib of a re-optimized neutral gold cluster was investigated at temperatures 0.5-300 K. The vibrational frequency of an optimized cluster was revealed by small atomic displacements using a numerical finite-differentiation method. This method was implemented using density-functional tight-binding (DFTB) approach. The desired set of system Eigen frequencies (3N -6) was obtained by diagonalization of the symmetric positive semi definite Hessian matrix. Our investigation revealed that the Cvib curve is strongly influenced by temperature, size, and structure and bond-order dependency. The effect of the range of interatomic forces is studied; especially the lower frequencies make a significant contribution to the heat capacity at low temperatures. In addition to that, we have exactly predicted the vibrational frequencies (ωi) which occur between 0.55 to 370.72 cm-1, depending on the nanoparticle morphology at T=0 for small neutral gold clusters AuN=3-20. This result has been proved and confirmed by the size effect values. It was found that beside the particle size, geometric shape, defect structure and an increase in asymmetry of nanoparticles effects on heat capacity. Surprisingly, the Boson peaks are typically ascribed to an excess density of vibrational states for the small clusters. Finally, temperature dependencies of the vibrational heat capacities of the re-optimized neutral gold clusters have been studied for the first time. more...
- Published
- 2017
- Full Text
- View/download PDF
5. Vibrational Heat Capacity of Gold Cluster AuN=14 at Low Temperatures
- Author
-
Springborg M and Vishwanathan K
- Subjects
Hessian matrix ,Gold cluster ,Range (particle radiation) ,010304 chemical physics ,Chemistry ,Nanotechnology ,Positive-definite matrix ,010402 general chemistry ,01 natural sciences ,Heat capacity ,Molecular physics ,0104 chemical sciences ,symbols.namesake ,Molecular vibration ,0103 physical sciences ,Cluster (physics) ,symbols ,Boson - Abstract
The vibrational heat capacity Cvib of a re-optimized neutral gold cluster AuN=14 was investigated at temperatures 0.5-300/950 K. The vibrational frequency of a optimized cluster was revealed by small atomic displacements using a numerical finite-differentiation method. This method was implemented using density-functional tight-binding (DFTB) approach. The desired set of system eigenfrequencies (3N-6) was obtained by diagonalization of the symmetric positive semidefinite Hessian matrix. Our investigation revealed that the Cvib curve is strongly influenced by temperature, size and structure dependency. The effect of the range of interatomic forces is studied, especially the lower frequencies make a significant contribution to the heat capacity at low temperatures. Surprisingly, the Boson peaks are typically ascribed to an excess density of vibrational states for the small clusters. Finally, temperature dependencies of the vibrational heat capacities of the re-optimized neutral gold cluster have been studied for the first time. more...
- Published
- 2016
- Full Text
- View/download PDF
6. Eu(II) luminescence in the perovskite host lattices KMgH3, NaMgH3 and mixed crystals LiBaxSr1-xH3
- Author
-
Kunkel, N., Meijerink, A., Springborg, M., Kohlmann, H., Sub Condensed Matter and Interfaces, and Condensed Matter and Interfaces
- Subjects
ENERGY ,EU2+ ,VIBRONIC TRANSITIONS ,DIFFRACTION ,DIVALENT EUROPIUM ,HYDRIDES - Abstract
Bright luminescence of Eu(II) doped into the cubic perovskites KMgH3 and mixed crystal compounds LiBaxSr(1-x)H(3) was observed and assigned to the 4f(6)5d-4f(7) emission of Eu2+. KMgH3: Eu2+ shows an extremely bright yellow emission, whereas the wavelength of the emission maximum in LiBaxSr(1-x)H(3): Eu2+ depends on the value of x and ranges from yellow to green. Furthermore, an extremely wide red shift in the emission energy is observed for the orthorhombically distorted perovskite NaMgH3: Eu2+. Additionally, we review the crystal structure of KMgH3 using density functional calculations. more...
- Published
- 2014
7. Eu(II) luminescence in the perovskite host lattices KMgH3, NaMgH3 and mixed crystals LiBaxSr1-xH3
- Author
-
Kunkel, N., Meijerink, A., Springborg, M., Kohlmann, H., Sub Condensed Matter and Interfaces, and Condensed Matter and Interfaces
- Subjects
Diffraction ,EU2+ ,Materials science ,Mixed crystal ,business.industry ,Doping ,General Chemistry ,Crystal structure ,DIFFRACTION ,HYDRIDES ,Red shift ,ENERGY ,Crystallography ,Wavelength ,Optics ,VIBRONIC TRANSITIONS ,Materials Chemistry ,business ,Luminescence ,DIVALENT EUROPIUM ,Perovskite (structure) - Abstract
Bright luminescence of Eu(II) doped into the cubic perovskites KMgH3 and mixed crystal compounds LiBaxSr(1-x)H(3) was observed and assigned to the 4f(6)5d-4f(7) emission of Eu2+. KMgH3: Eu2+ shows an extremely bright yellow emission, whereas the wavelength of the emission maximum in LiBaxSr(1-x)H(3): Eu2+ depends on the value of x and ranges from yellow to green. Furthermore, an extremely wide red shift in the emission energy is observed for the orthorhombically distorted perovskite NaMgH3: Eu2+. Additionally, we review the crystal structure of KMgH3 using density functional calculations. more...
- Published
- 2014
8. Ab initio study of metastable layered perovskites R 2Ti 2O 7 (R = Sm and Gd)
- Author
-
Sayede, Adlane, Bruyer, E., Springborg, M., UCCS Équipe Couches Minces & Nanomatériaux, Unité de Catalyse et Chimie du Solide - UMR 8181 (UCCS), Centrale Lille Institut (CLIL)-Université d'Artois (UA)-Centrale Lille-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Lille-Centrale Lille Institut (CLIL)-Université d'Artois (UA)-Centrale Lille-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Lille, and Université d'Artois (UA)-Centrale Lille-Institut de Chimie du CNRS (INC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université d'Artois (UA)-Centrale Lille-Institut de Chimie du CNRS (INC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS) more...
- Subjects
[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,[CHIM]Chemical Sciences ,[CHIM.MATE]Chemical Sciences/Material chemistry ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience; no abstract
- Published
- 2012
- Full Text
- View/download PDF
9. Structural and energetic properties of nickel clusters: $2 \le N \le 150$
- Author
-
Grigoryan, V. G. and Springborg, M.
- Subjects
Chemical Physics (physics.chem-ph) ,Physics - Chemical Physics ,FOS: Physical sciences ,Physics - Atomic and Molecular Clusters ,Atomic and Molecular Clusters (physics.atm-clus) - Abstract
The four most stable structures of Ni$_N$ clusters with $N$ from 2 to 150 have been determined using a combination of the embedded-atom method in the version of Daw, Baskes and Foiles, the {\it variable metric/quasi-Newton} method, and our own {\it Aufbau/Abbau} method. A systematic study of energetics, structure, growth, and stability of also larger clusters has been carried through without more or less severe assumptions on the initial geometries in the structure optimization, on the symmetry, or on bond lengths. It is shown that cluster growth is predominantly icosahedral with $islands$ of {\it fcc}, {\it tetrahedral} and {\it decahedral} growth. For the first time in unbiased computations it is found that Ni$_{147}$ is the multilayer (third Mackay) icosahedron. Further, we point to an enhanced ability of {\it fcc} clusters to compete with the icosahedral and decahedral structures in the vicinity of N=79. In addition, it is shown that conversion from the {\it hcp}/anti-Mackay kind of icosahedral growth to the {\it fcc}/Mackay one occurs within a transition layer including several cluster sizes. Moreover, we present and apply different analytical tools in studying structural and energetic properties of such a large class of clusters. These include means for identifying the overall shape, the occurrence of atomic shells, the similarity of the clusters with, e.g., fragments of the {\it fcc} crystal or of a large icosahedral cluster, and a way of analysing whether the $N$-atom cluster can be considered constructed from the $(N-1)$-atom one by adding an extra atom. In addition, we compare in detail with results from chemical-probe experiment. Maybe the most central result is that first for clusters with $N$ above 80 general trends can be identified., 37 pages, 11 figures more...
- Published
- 2004
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.