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Full-Text Articles in Physics
Adaptive Spline Fitting With Particle Swarm Optimization, Soumya Mohanty, Ethan Fahnestock
Adaptive Spline Fitting With Particle Swarm Optimization, Soumya Mohanty, Ethan Fahnestock
Physics and Astronomy Faculty Publications and Presentations
In fitting data with a spline, finding the optimal placement of knots can significantly improve the quality of the fit. However, the challenging high-dimensional and non-convex optimization problem associated with completely free knot placement has been a major roadblock in using this approach. We present a method that uses particle swarm optimization (PSO) combined with model selection to address this challenge. The problem of overfitting due to knot clustering that accompanies free knot placement is mitigated in this method by explicit regularization, resulting in a significantly improved performance on highly noisy data. The principal design choices available in the method …
Enhanced Magnetic Moments Of Alkali Metal Coated Sc Clusters: New Magnetic Superatoms, Kalpataru Pradhan, J. Ulises Reveles, Prasenjit Sen, S. N. Khanna
Enhanced Magnetic Moments Of Alkali Metal Coated Sc Clusters: New Magnetic Superatoms, Kalpataru Pradhan, J. Ulises Reveles, Prasenjit Sen, S. N. Khanna
Physics Publications
It is shown that the magnetic moments of Sc atoms can be significantly enhanced by combining them with alkali atoms. We present results of first principles electronic structure calculations of ScNan (1≤n≤12) clusters that indicate that a ScNa12 cluster consisting of a Sc atom surrounded by 12 Na atoms forming a compact icosahedral structure has a spin magnetic moment of 3μB that is three times that of an isolated Sc atom. This unusual behavior is analyzed in terms of the filling of the supershells 1S, 1P,… controlled by the nature and size of the alkali atoms and the more localized …
The Applicability Of Three-Dimensional Aromaticity In Bisnn- Zintl Analogues, Penee A. Clayborne, Ujjwal Gupta, Arthur C. Reber, Joshua J. Melko, Shiv N. Khanna, A. W. Castleman Jr.
The Applicability Of Three-Dimensional Aromaticity In Bisnn- Zintl Analogues, Penee A. Clayborne, Ujjwal Gupta, Arthur C. Reber, Joshua J. Melko, Shiv N. Khanna, A. W. Castleman Jr.
Physics Publications
Three-dimensional aromaticity is shown to play a role in the stability of deltahedral Zintl clusters and here we examine the connection between aromaticity and stability. In order to gain further insight, we have studied Zintl analogs comprised of bismuthdopedtin clusters with photoelectron spectroscopy and theoretical methods. To assign aromaticity, we examine the ring currents induced around the cage by using the nucleus independent chemical shift. In the current study, BiSn4− is a stable cluster and fits aromatic criteria, while BiSn5− is found to fit antiaromatic criteria and has reduced stability. The more stable clusters exhibit an aromatic character which originates …
Stability And Magnetic Properties Of T2sin (T=Cr,Mn,1≤N≤8) Clusters, R. Robles, Shiv N. Khanna, A. W. Castleman Jr
Stability And Magnetic Properties Of T2sin (T=Cr,Mn,1≤N≤8) Clusters, R. Robles, Shiv N. Khanna, A. W. Castleman Jr
Physics Publications
First-principles studies on the geometry, electronic structure, and magnetic properties of neutral and anionic Cr2Sin and Mn2Sin (1≤n≤8) have been carried out within a gradient corrected density-functional framework. We find that Cr2Sin clusters containing up to five Si atoms and Mn2Sin clusters containing up to eight Si atoms are all marked by finite local spin moments at the transition-metal site that order ferromagnetically or antiferromagnetically depending on the size and the charged state. Our studies of the variation in the binding energy upon addition of successive Si atoms and the gap between the highest occupied molecular orbital and the lowest …
Structure And Stability Of Co-N(Pyridine)(M)(-) Clusters: Absence Of Metal Inserted Structures, B. Douglas Edmonds, A. K. Kandalam, S. N. Khanna, X. Li, A. Grubisic, I. Khanna, K. H. Bowen
Structure And Stability Of Co-N(Pyridine)(M)(-) Clusters: Absence Of Metal Inserted Structures, B. Douglas Edmonds, A. K. Kandalam, S. N. Khanna, X. Li, A. Grubisic, I. Khanna, K. H. Bowen
Physics Publications
A synergistic approach combining the experimental photoelectron spectroscopy and theoretical electronic structure studies is used to probe the geometrical structure and the spin magnetic moment of Con(pyridine)−m clusters. It is predicted that the ground state of Co(pyridine)− is a structure where the Co atom is inserted in a CH bond. However, the insertion is marked by a barrier of 0.33eV that is not overcome under the existing experimental conditions resulting in the formation of a structure where Co occupies a site above the pyridine plane. For Co2(pyridine)−, a ground-state structure is predicted in which the Co2 diametric moiety is inserted …
Magnetic Properties Of Al, V, Mn, And Ru Impurities In Fe–Co Alloys, B. V. Reddy, S. C. Deevi, S. N. Khanna
Magnetic Properties Of Al, V, Mn, And Ru Impurities In Fe–Co Alloys, B. V. Reddy, S. C. Deevi, S. N. Khanna
Physics Publications
Theoretical studies on the magnetic properties of impurities in Fe–Co alloys have been carried out using a molecular-orbital approach within a gradient corrected density functional formalism. The defected alloy is modeled by a large cluster and the calculations on the ordered alloy are used to show that a cluster containing 67 atoms can provide quantitative information on the local magnetic moment. It is found that although bulk Al, V, and Ru are nonmagnetic, all the impurities carry finite moments. While Al and V impurities couple antiferromagnetically, Ru impurities couple ferromagnetically to the host sites. It is shown that the observed …
Electronic-Structure-Based Investigation Of Magnetism In The Fe8 Molecular Magnet, Mark R. Pederson, Jens Kortus, S. N. Khanna
Electronic-Structure-Based Investigation Of Magnetism In The Fe8 Molecular Magnet, Mark R. Pederson, Jens Kortus, S. N. Khanna
Physics Publications
We have performed density-functional-based electronic structure calculations on a single Fe8 molecular nanomagnet. Our calculated total moments and local moments are in excellent agreement with experiment. By including spin–orbit coupling we determine the easy, medium, and hard axes and find the ordering of the principle axes also agrees with experiment. From our calculated anisotropy Hamiltonian, we calculate the oscillations in the tunnel splittings and compare to the experimental results.
Reactivity And Electronic Structure Of Aluminum Clusters: The Aluminum-Nitrogen System, B. D. Leskiw, A. W. Castleman Jr., C. Ashman, S. N. Khanna
Reactivity And Electronic Structure Of Aluminum Clusters: The Aluminum-Nitrogen System, B. D. Leskiw, A. W. Castleman Jr., C. Ashman, S. N. Khanna
Physics Publications
The stability of anionic aluminum–nitrogen clusters has been examined and Al2N−, Al3N−2,Al5N−2, Al6N−3, Al8N−3, and Al9N−2 are found to be particularly stable. Theoreticaldensity functional calculations on neutral and anionic AlnN (n=1–8) clusters were performed and the stability and reaction energetics with oxygen examined. Clusters requiring less than 5.7 eV to remove an electron and an Al atom are shown to be resistant to the reaction with oxygen.
Geometry, Electronic Structure, And Energetics Of Copper-Doped Aluminum Clusters, S. N. Khanna, C. Ashman, B. K. Rao, P. Jena
Geometry, Electronic Structure, And Energetics Of Copper-Doped Aluminum Clusters, S. N. Khanna, C. Ashman, B. K. Rao, P. Jena
Physics Publications
Using density functional theory and generalized gradient approximation for exchange-correlation potential, we have calculated the equilibrium geometries and energetics of neutral and negatively charged AlnCu (n=11,12,13,14) clusters. Unlike the alkali atom-doped aluminum clusters in the same size range, the copper atom resides inside the aluminum cluster cage. Furthermore, the 3d and 4s energy levels of Cu hybridize with the valence electrons of Al causing a redistribution of the molecular orbital energy levels of the Aln clusters. However, this redistribution does not affect the magic numbers of AlnCu clusters that could be derived by assuming that Cu donates one electron to …
Magnetic Coupling In Neutral And Charged Cr-2, Mn-2, And Crmn Dimers, N. Desmarais, F. A. Reuse, S. N. Khanna
Magnetic Coupling In Neutral And Charged Cr-2, Mn-2, And Crmn Dimers, N. Desmarais, F. A. Reuse, S. N. Khanna
Physics Publications
Theoreticalab initio studies of neutral, cationic and anionic Cr2, Mn2, and CrMn dimers have been carried out to explore the progression of magnetic coupling with the number of electrons. It is shown that while Cr2 and Cr−2 have antiferromagnetically coupled atomic spins, Cr+2 has a ferromagneticground state closely followed by an antiferromagnetic state. On the other hand, all Mn2 dimers are ferromagnetic, irrespective of the charge. The neutral CrMn is ferrimagnetic while the charged CrMn are antiferromagnetic. In all cases, the charged dimers are found to be more stable than the neutral ones. The results are compared with available …
Theoretical Calculations Of Magnetic Order And Anisotropy Energies In Molecular Magnets, M. R. Pederson, D. V. Porezag, J. Kortus, S. N. Khanna
Theoretical Calculations Of Magnetic Order And Anisotropy Energies In Molecular Magnets, M. R. Pederson, D. V. Porezag, J. Kortus, S. N. Khanna
Physics Publications
We present theoretical electronic structure calculations on the nature of electronic states and the magnetic coupling in the Mn12O12 free cluster and the Mn12O12(RCOO)16(H2O)4 molecular magnetic crystal. The calculations have been performed with the all-electron full-potential NRLMOL code. We find that the free Mn12O12cluster relaxes to an antiferromagneticcluster with no net moment. However, when coordinated by sixteen HCOO ligands and four H2O groups, as it is in the molecular crystal, we find that the ferrimagnetic ordering and geometrical and magnetic structure observed in the experiments is restored. Local Mn moments for the free and ligandated molecular magnets are presented and …