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2004

Virginia Commonwealth University

Articles 1 - 16 of 16

Full-Text Articles in Physics

Metastability Of A Gold Nanoring: Density-Functional Calculations, Q. Sun, Q. Wang, Puru Jena, R. Note, J-Z. Yu, Y. Kawazoe Jan 2004

Metastability Of A Gold Nanoring: Density-Functional Calculations, Q. Sun, Q. Wang, Puru Jena, R. Note, J-Z. Yu, Y. Kawazoe

Physics Publications

First-principles calculations based on gradient corrected density functional theory show that a cluster of as few as 90 gold atoms can be stabilized in a ring structure having fcc (111) motif with the binding energy/atom and interatomic distance approaching 91% and 96% of the bulk values, respectively. Although the ring structure lies 0.139eV/atom higher in energy than a polyicosahedral structure, the calculated frequencies are real. Thus under appropriate experimental conditions it may still be possible to synthesize a metastable form of gold nanoring, as found in the recent experiment.

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Magnetic Isomers And Local Moment Distribution In Mn5o And Mn6o Clusters, N. O. Jones, Shiv N. Khanna, T. Baruah, M. R. Pederson, W.-J. Zheng, J. M. Nilles, K. H. Bowen Jan 2004

Magnetic Isomers And Local Moment Distribution In Mn5o And Mn6o Clusters, N. O. Jones, Shiv N. Khanna, T. Baruah, M. R. Pederson, W.-J. Zheng, J. M. Nilles, K. H. Bowen

Physics Publications

A synergistic approach combining the experimental photoelectron spectroscopy and theoretical electronic structure studies is used to demonstrate the existence of magnetic isomers as well as configurations having comparable binding energies, identical spins, and yet differing in the distribution of local moments (called isomags). Our studies carried out on Mn5O and Mn6O clusters show that while the O atom occupies either bridge or hollow site with a binding energy of 6.88eV in Mn5, it prefers a hollow site with a binding energy of 7.18eV in Mn6 clusters. Mn5O is shown to possess two magnetic isomers with total spins of 13 and …

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Spectroscopic Signature Of Magnetic Bistability In Mn2oà Anions And Its Implications For Piezomagnetism At The Nanoscale, Shiv N. Khanna, Puru Jena, W.-J. Zheng, J. M. Nilles, K. H. Bowen Jan 2004

Spectroscopic Signature Of Magnetic Bistability In Mn2oà Anions And Its Implications For Piezomagnetism At The Nanoscale, Shiv N. Khanna, Puru Jena, W.-J. Zheng, J. M. Nilles, K. H. Bowen

Physics Publications

A synergistic study, using gradient corrected density functional theory and photoelectron spectroscopy, shows that the presence of oxygen can fundamentally alter the interaction between two Mn atoms. The normally weak interaction between two Mn atoms exhibits strong bonding when an oxygen atom is added to form Mn2O. This allows the atomiclike magnetic moments of each Mn atom to couple either ferromagnetically or antiferromagnetically depending on whether Mn2O is anionic or neutral. Furthermore, the Mn2O− anion is found to possess an antiferromagnetic isomer that lies only 0.01 eV above its nearly degenerate ferromagnetic ground state. The possibility of exploiting this magnetic …

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Hydrogen Adsorption And Magnetic Behavior Of Fen And Con Clusters: Controlling The Magnetic Moment And Anisotropy One Atom At A Time, N. O. Jones, M. R. Beltran, Shiv N. Khanna, T. Baruah, M. R. Pederson Jan 2004

Hydrogen Adsorption And Magnetic Behavior Of Fen And Con Clusters: Controlling The Magnetic Moment And Anisotropy One Atom At A Time, N. O. Jones, M. R. Beltran, Shiv N. Khanna, T. Baruah, M. R. Pederson

Physics Publications

Theoretical studies to investigate the effect of H absorption on the magnetic moment of small Fen and Con clusters have been carried out using gradient corrected density-functional approach. Our studies on clusters containing up to four transition metal and 2 H atoms show that the successive addition of H atoms can lead to monotonic or oscillatory change from the free cluster magnetic moment. A detailed analysis of the density of electronic states shows that the variations in the magnetic moment can be related to the location of the lowest unoccupied molecular orbital in the parent cluster. It is shown that …

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Energetics And Local Spin Magnetic Moment Of Single 3,4d Impurities Encapsulated In An Icosahedral Au12 Cage, Shan-Ying Wang, Jing-Zhi Yu, Hiroshi Mizuseki, Qiang Sun, Chong-Yu Wang, Yoshiyuki Kawazoe Jan 2004

Energetics And Local Spin Magnetic Moment Of Single 3,4d Impurities Encapsulated In An Icosahedral Au12 Cage, Shan-Ying Wang, Jing-Zhi Yu, Hiroshi Mizuseki, Qiang Sun, Chong-Yu Wang, Yoshiyuki Kawazoe

Physics Publications

The energetics and local spin magnetic moment of a single 3,4d impurity (Sc-Ni, Y-Pd) encapsulated in an icosahedral Au12 cage have been studied theoretically by using a real-space first-principles cluster method with generalized gradient approximation for exchange-correlation functional. The relativistic effect is considered by scalar relativistic pseudopotentials. All doped clusters show unexpected large relative binding energies compared with icosahedral Au13cluster. The smallest and the largest values appear at Pd and Zr, 2.186 and 7.791eV per cluster, respectively, indicating doping could stabilize the icosahedral Au12 cage and promote the formation of a new binary alloy cluster. Comparatively large magnetic moments are …

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Carrier-Mediated Ferromagnetism In N Codoped (Zn,Mn)O (101¯0) Thin Films, Q. Wang, Q. Sun, Puru Jena, Y. Kawazoe Jan 2004

Carrier-Mediated Ferromagnetism In N Codoped (Zn,Mn)O (101¯0) Thin Films, Q. Wang, Q. Sun, Puru Jena, Y. Kawazoe

Physics Publications

Using first principles calculations based on the density functional theory and generalized gradient approximation we show that the ground state of Mn doped ZnO (101¯0) thin film changes from antiferromagnetic to ferromagnetic when codoped with N. The ferromagnetic coupling between Mn spins arises due to the overlap between N 2p and Mn 3d electrons in the spin up band, rendering the system half-metallic character.

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Classical Stern-Gerlach Profiles Of Mn5 And Mn6 Clusters, N. O. Jones, Shiv N. Khanna, Tunna Baruah, M. R. Pederson Jan 2004

Classical Stern-Gerlach Profiles Of Mn5 And Mn6 Clusters, N. O. Jones, Shiv N. Khanna, Tunna Baruah, M. R. Pederson

Physics Publications

Mn5 and Mn6 clusters have recently been found to exhibit Stern-Gerlach profiles marked by a central peak that broadens with the increasing field gradient. The profiles neither exhibit a reminiscence of space quantization as observed through a splitting of beams for the case of free atoms, nor a net deflection characteristic of superparamagnetic relaxations observed in other transition metal clusters. It is proposed that this new behavior results from a weak coupling of localized atomic moments. ab initio electronic structure studies are carried out to show that a Mn5cluster has isomers with spin magnetic moments of 3μB, 13μB, and 23μBwhile …

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Magnetism And Energetics Of Mn-Doped Zno (101¯0) Thin Films, Q. Wang, Q. Sun, B. K. Rao, Puru Jena Jan 2004

Magnetism And Energetics Of Mn-Doped Zno (101¯0) Thin Films, Q. Wang, Q. Sun, B. K. Rao, Puru Jena

Physics Publications

First-principles calculations based on gradient corrected density functional theory are performed on Mn-doped ZnO thin film. Magnetism and energetics are studied for two Mn concentrations and varying Mn configurations. It is found that in the dilute limit when Mn atoms are far apart, the ferro-magnetic and antiferromagnetic states are energetically nearly degenerate. The resulting fluctuation would, therefore, make the system paramagnetic as found in the experiment. But, as the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around oxygen. For such a configuration, the antiferromagnetic coupling between Mn atoms is …

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Interactions Of Au Cluster Anions With Oxygen, Qiang Sun, Puru Jena, Young Dok Kim, Matthias Fischer, Gerd Ganteför Jan 2004

Interactions Of Au Cluster Anions With Oxygen, Qiang Sun, Puru Jena, Young Dok Kim, Matthias Fischer, Gerd Ganteför

Physics Publications

Experimental and theoretical evidence is presented for the nondissociative chemisorption of O2on free Au cluster anions (Au−n, n=number of atoms) with n=2, 4, 6 at room temperature, indicating that the stabilization of the activated di-oxygen species is the key for the unusual catalytic activities of Au-based catalysts. In contrast to Au−n with n=2, 4, 6, O2 adsorbs atomically on Aumonomer anions. For the Aumonomer neutral, calculations based on density functional theory reveal that oxygen should be molecularly bound. On Au dimer and tetramer neutrals, oxygen is molecularly bound with the O–O bond being less activated with respect to their …

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Competition Between Linear And Cyclic Structures In Monochromium Carbide Clusters Crcn- And Crcn (N=2-8): A Photoelectron Spectroscopy And Density Functional Study, Hua-Jin Zhai, Lai-Sheng Wang, P. Jena, G. L. Gutsev, C. W. Bauschlicher Jr. Jan 2004

Competition Between Linear And Cyclic Structures In Monochromium Carbide Clusters Crcn- And Crcn (N=2-8): A Photoelectron Spectroscopy And Density Functional Study, Hua-Jin Zhai, Lai-Sheng Wang, P. Jena, G. L. Gutsev, C. W. Bauschlicher Jr.

Physics Publications

Photoelectron spectroscopy (PES) is combined with density functional theory (DFT) to study the monochromium carbide clusters CrC−n and CrCn (n=2–8). Well-resolved PES spectra were obtained, yielding structural, electronic, and vibrational information about both the anionic and neutral clusters. Experimental evidence was observed for the coexistence of two isomers for CrC−2, CrC−3, CrC−4, and CrC−6. Sharp and well-resolved PES spectra were observed for CrC−n (n=4,6,8), whereas broad spectra were observed for CrC−5 and CrC−7. Extensive DFT calculations using the generalized gradient approximation were carried out for the ground and low-lying excited states of all the CrC−n and CrCn species, as well …

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Geometry And Electronic Structure Of V-N(Bz)(M) Complexes, Anil K. Kandalam, B. K. Rao, P. Jena, Ravindra Pandey Jan 2004

Geometry And Electronic Structure Of V-N(Bz)(M) Complexes, Anil K. Kandalam, B. K. Rao, P. Jena, Ravindra Pandey

Physics Publications

First-principles calculations based on the generalized gradient approximation to the density functional theory are performed to explore the global geometries, ground-state spin multiplicities, relative stabilities, and energetics of neutral and anionic Vn(Bz)m (n51 – 3, m51 – 4, with n ,m) complexes. The calculated results show that the Vn(benzene)m complexes clearly prefer sandwich structures to rice-ball structures. The ground-state spin multiplicities of the Vn(benzene)n11 complexes increased linearly with the size of the system (i.e., n). In the anionic complexes, the V(benzene)2 complex is found to be unstable against the autodetachment of the extra electron. The energy difference between adiabatic and …

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Periodic Table Of 3d-Metal Dimers And Their Ions, G. L. Gutsev, M. D. Mochena, P. Jena, C. W. Bauchlicher Jr., H. Partridge Iii Jan 2004

Periodic Table Of 3d-Metal Dimers And Their Ions, G. L. Gutsev, M. D. Mochena, P. Jena, C. W. Bauchlicher Jr., H. Partridge Iii

Physics Publications

The ground states of the mixed 3d-metal dimers TiV, TiCr, TiMn, TiFe, TiCo, TiNi, TiCu, TiZn, VCr, VMn, VFe, VCo, VNi, VCu, VZn, CrMn, CrFe, CrCo, CrNi, CrCu, CrZn, MnFe, MnCo, MnNi, MnCu, MnZn, FeCo, FeNi, FeCu, FeZn, CoNi, CoCu, CoZn, NiCu, NiZn, and CuZn along with their singly negatively and positively charged ions are assigned based on the results of computations using density functional theory with generalized gradient approximation for the exchange-correlation functional. Except for TiCo and CrMn, our assignment agrees with experiment. Computed spectroscopic constants (re,ωe,Do) are in fair agreement with experiment. The ground-state spin multiplicities of all …

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Appearance Of Bulk Properties In Small Tungsten Oxide Clusters, Q. Sun, B. K. Rao, P. Jena, D. Stolcic, Y. D. Kim, Gerd Gantefor, A. W. Castleman Jr. Jan 2004

Appearance Of Bulk Properties In Small Tungsten Oxide Clusters, Q. Sun, B. K. Rao, P. Jena, D. Stolcic, Y. D. Kim, Gerd Gantefor, A. W. Castleman Jr.

Physics Publications

Contrary to the conventional understanding that atomic clusters usually differ in properties and structure from the bulk constituents of which they are comprised, we show that even a dimer of tungsten oxide (WO3)2 possesses bulklike features and the geometry of a small cluster containing only 4 tungsten and 12 oxygen atoms bears the hallmarks of crystalline tungsten oxide, WO3. This observation, based on a synergistic approach involving mass distributions under quasisteady state conditions, photoelectron spectroscopy, and first principles molecular orbital theory, not only illustrates the existence of a class of strongly covalent or ionic materials whose embryonic forms are tiny …

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Formation And Properties Of Halogenated Aluminum Clusters, D. E. Bergeron, A. W. Castleman Jr., T. Morisato, S. N. Khanna Jan 2004

Formation And Properties Of Halogenated Aluminum Clusters, D. E. Bergeron, A. W. Castleman Jr., T. Morisato, S. N. Khanna

Physics Publications

The fast-flow tube reaction apparatus was employed to study the halogenation of aluminum clusters. For reactions with HX (X=Cl, Br, and I), acid-etching pathways are evident, and we present findings for several reactions, whereby AlnX− generation is energetically favorable. Tandem reaction experiments allowed us to establish that for AlnCl−, AlnI−, and AlnI−2, species with n=6, 7, and 15 are particularly resistant to attack by oxygen. Further, trends in reactivity suggest that, in general, iodine incorporation leaves the aluminum clusters’ electronic properties largely unperturbed. Ab initio calculations were performed to better interpret reaction mechanisms and elucidate the characteristics of the products. …

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First-Principles Study Of Magnetism In (112̄0) Zn1−Xmnxo Thin Film, Q. Wang, Puru Jena Jan 2004

First-Principles Study Of Magnetism In (112̄0) Zn1−Xmnxo Thin Film, Q. Wang, Puru Jena

Physics Publications

First-principles calculations of total energies and magnetism of Zn1−xMnxOthin film are performed by simulating it with a slab consisting of seven layers along (112̄0). It is shown that a single Mn atom shows very little preference for the site it occupies. This is consistent with the experimental finding that Mn atoms are homogeneously distributed in ZnO films. As the concentration of Mn atoms increases, antiferromagnetic coupling between Mn atoms becomes more favorable, and there is a tendency for Mn atoms to form clusters around oxygen, in agreement with recent experiments.

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Ferromagnetism In Cr-Doped Gan: A First-Principles Calculation, G. P. Das, B. K. Rao, Puru Jena Jan 2004

Ferromagnetism In Cr-Doped Gan: A First-Principles Calculation, G. P. Das, B. K. Rao, Puru Jena

Physics Publications

Electronic structure, energy bands, and magnetic properties of Cr-doped GaN have been calculated from first principles using a 32 atom supercell within the frame work of linearized muffin-tin orbital tight binding method and gradient-corrected density-functional theory. The coupling between Cr atoms is found to be ferromagnetic with a magnetic moment of 2.69μB at each Cr site. The magnetic moments of Ga and N sites are rather small, namely, 0.025μB and −0.025μB, respectively, yielding a total moment of 6μB per supercell. Parallel calculations done on small clusters of Cr-doped GaN also yield similar results indicating that magnetic coupling between Cr atoms …

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