50 research outputs found
Does hybrid density functional theory predict a non-magnetic ground state for delta-Plutonium?
Hybrid density functionals, which replaces a fraction of density functional
theory (DFT) exchange with exact Hartree-Fock (HF) exchange, have been used to
study the structural, magnetic, and electronic properties of delta-Plutonium.
The fractions of exact Hartree-Fock exchange used were 25%, 40%, and 55%.
Compared to the pure PBE functional, the lattice constants expanded with
respect to the experimental value when the PBE-HF hybrid functionals were
applied. A non-magnetic ground state was realized for 55% HF contribution;
otherwise the ground state was anti-ferromagnetic. The 5f electrons tend to
exhibit slight delocalization or itinerancy for the pure PBE functional and
well-defined localization for the hybrid functionals, with the degree of 5f
electron localization increasing with the amount of HF exchange. Overall, the
performance of the hybrid density functionals do not seem superior to pure
density functionals for delta-Plutonium.Comment: 24 pages (double spaced), 5 figures, 1 tabl
Temporal Learning in Video Data Using Deep Learning and Gaussian Processes
This paper presents an approach for data-driven modeling of hidden, stationary temporal dynamics in sequential images or videos using deep learning and Bayesian non-parametric techniques. In particular, a deep Convolutional Neural Network (CNN) is used to extract spatial features in an unsupervised fashion from individual images and then, a Gaussian process is used to model the temporal dynamics of the spatial features extracted by the deep CNN. By decomposing the spatial and temporal components and utilizing the strengths of deep learning and Gaussian processes for the respective sub-problems, we are able to construct a model that is able to capture complex spatio-temporal phenomena while using relatively small number of free parameters. The proposed approach is tested on high-speed grey-scale video data obtained of combustion flames in a swirl-stabilized combustor, where certain protocols are used to induce instability in combustion process. The proposed approach is then used to detect and predict the transition of the combustion process from stable to unstable regime. It is demonstrated that the proposed approach is able to detect unstable flame conditions using very few frames from high-speed video. This is useful as early detection of unstable combustion can lead to better control strategies to mitigate instability. Results from the proposed approach are compared and contrasted with several baselines and recent work in this area. The performance of the proposed approach is found to be significantly better in terms of detection accuracy, model complexity and lead-time to detection
Density functional study of the actinide nitrides
The full potential all electron linearized augmented plane wave plus local
orbitals (FP-LAPW + lo) method, as implemented in the suite of software WIEN2K,
has been used to systematically investigate the structural, electronic, and
magnetic properties of the actinide compounds AnN (An = Ac, Th, Pa, U, Np, Pu,
Am). The theoretical formalism used is the generalized gradient approximation
to density functional theory (GGA-DFT) with the Perdew-Burke-Ernzerhof (PBE)
exchange-correlation functional. Each compound has been studied at six levels
of theory: non-magnetic (NM), non-magnetic with spin-orbit coupling (NM+SOC),
ferromagnetic (FM), ferromagnetic with spin-orbit coupling (FM+SOC),
anti-ferromagnetic (AFM), and anti-ferromagnetic with spin-orbit coupling
(AFM+SOC). The structural parameters, bulk moduli, densities of states, and
charge distributions have been computed and compared to available experimental
data and other theoretical calculations published in the literature. The total
energy calculations indicate that the lowest energy structures of AcN, ThN, and
PaN are degenerate at the NM+SOC, FM+SOC, and AFM+SOC levels of theory with
vanishing total magnetic moments in the FM+SOC and AFM+SOC cases, making the
ground states essentially non-magnetic with spin-orbit interaction. The ground
states of UN, NpN, PuN, and AmN are found to be FM+SOC at the level of theory
used in the present computations. The nature of the interactions between the
actinide metals and nitrogen atom, and the implications on 5f electron
delocalization and localization are discussed in detail.Comment: 5 tables, 12 figure
Host-guest interaction of cucurbit[7]uril with para-nitrophenol: A weakly binding inclusion complex
Host-guest interaction between water soluble rigid molecular container cucurbit[7]uril (CB[7]) and a water soluble organic guest para-nitrophenol (PNP) has been investigated using 1H NMR spectroscopy and isothermal titration calorimetry. The stoichiometry, binding constant and other thermodynamic parameters of complexation have been obtained which show the formation of weakly binding 1:1 inclusion complex resulting from enthalpy-entropy compensation. Cyclic voltammetry study of PNP-CB[7] complex in acidic pH reveals a large cathodic shift in the reduction potentials of PNP, indicating either stabilization of PNP or destabilization of the electro-reduced product inside CB[7] cavity
A Full-Potential-Linearized-Augmented-Plane-Wave Electronic Structure Study of delta-Plutonium and the (001) Surface
The electronic and geometric properties of bulk fcc delta-plutonium and the
quantum size effects in the surface energies and the work functions of the
(001) ultra thin films (UTF) up to 7 layers have been investigated with
periodic density functional theory calculations within the full-potential
linearized augmented-plane wave (FP-LAPW) approach as implemented in the WIEN2k
package. Our calculated equilibrium atomic volume of 178.3 a.u.^3 and bulk
modulus of 24.9 GPa at the fully relativistic level of theory, i.e.
spin-polarization and spin-orbit coupling included, are in good agreement with
the experimental values of 168.2 a.u.^3 and 25 GPa (593 K), respectively. The
calculated equilibrium lattice constants at different levels of approximation
are used in the surface properties calculations for the thin films. The surface
energy is found to be rapidly converged with the semi-infinite surface energy
predicted to be 0.692eV at the fully-relativistic level.Comment: 27 pages,8 figure