36 research outputs found
GW quasiparticle calculations with spin-orbit coupling for the light actinides
We report on the importance of GW self-energy corrections for the electronic
structure of light actinides in the weak-to-intermediate coupling regime. Our
study is based on calculations of the band structure and total density of
states of Np, U, and Pu using a one-shot GW approximation that includes
spin-orbit coupling within a full potential LAPW framework. We also present RPA
screened effective Coulomb interactions for the f-electron orbitals for
different lattice constants, and show that there is an increased contribution
from electron-electron correlation in these systems for expanded lattices. We
find a significant amount of electronic correlation in these highly localized
electronic systems.Comment: Accepted and to appear in Phys. Rev.
Optical Properties of Organometallic Perovskite: An ab initio Study using Relativistic GW Correction and Bethe-Salpeter Equation
In the development of highly efficient photovoltaic cells, solid perovskite
systems have demonstrated unprecedented promise, with the figure of merit
exceeding nineteen percent of efficiency. In this paper, we investigate the
optical and vibrational properties of organometallic cubic perovskite
CH3NH3PbI3 using first-principles calculations. For accurate theoretical
description, we go beyond conventional density functional theory (DFT), and
calculated optical conductivity using relativist quasi-particle (GW)
correction. Incorporating these many-body effects, we further solve
Bethe-Salpeter equations (BSE) for excitons, and found enhanced optical
conductivity near the gap edge. Due to the presence of organic methylammonium
cations near the center of the perovskite cell, the system is sensitive to low
energy vibrational modes. We estimate the phonon modes of CH3NH3PbI3 using
small displacement approach, and further calculate the infrared absorption (IR)
spectra. Qualitatively, our calculations of low-energy phonon frequencies are
in good agreement with our terahertz measurements. Therefore, for both energy
scales (around 2 eV and 0-20 meV), our calculations reveal the importance of
many-body effects and their contributions to the desirable optical properties
in the cubic organometallic perovskites system.Comment: 5 pages, 4 figure
Vibrational Signatures in the THz Spectrum of 1,3-DNB: A First-Principles and Experimental Study
Understanding the fundamental processes of light-matter interaction is
important for detection of explosives and other energetic materials, which are
active in the infrared and terahertz (THz) region. We report a comprehensive
study on electronic and vibrational lattice properties of structurally similar
1,3-dinitrobenzene (1,3- DNB) crystals through first-principles electronic
structure calculations and THz spectroscopy measurements on polycrystalline
samples. Starting from reported x-ray crystal structures, we use
density-functional theory (DFT) with periodic boundary conditions to optimize
the structures and perform linear response calculations of the vibrational
properties at zero phonon momentum. The theoretically identified normal modes
agree qualitatively with those obtained experimentally in a frequency range up
to 2.5 THz and quantitatively at much higher frequencies. The latter
frequencies are set by intra-molecular forces. Our results suggest that van der
Waals dispersion forces need to be included to improve the agreement between
theory and experiment in the THz region, which is dominated by intermolecular
modes and sensitive to details in the DFT calculation. An improved comparison
is needed to assess and distinguish between intra- and intermolecular
vibrational modes characteristic of energetic materials.Comment: 5 pages, 5 figure
Death Associated Protein Kinase (DAPK) -mediated neurodegenerative mechanisms in nematode excitotoxicity
Background: Excitotoxicity (the toxic overstimulation of neurons by the excitatory transmitter Glutamate) is a central process in widespread neurodegenerative conditions such as brain ischemia and chronic neurological diseases. Many mechanisms have been suggested to mediate excitotoxicity, but their significance across diverse excitotoxic scenarios remains unclear. Death Associated Protein Kinase (DAPK), a critical molecular switch that controls a range of key signaling and cell death pathways, has been suggested to have an important role in excitotoxicity. However, the molecular mechanism by which DAPK exerts its effect is controversial. A few distinct mechanisms have been suggested by single (sometimes contradicting) studies, and a larger array of potential mechanisms is implicated by the extensive interactome of DAPK.
Results: Here we analyze a well-characterized model of excitotoxicity in the nematode C. elegans to show that DAPK is an important mediator of excitotoxic neurodegeneration across a large evolutionary distance. We further show that some proposed mechanisms of DAPK’s action (modulation of synaptic strength, involvement of the DANGER-related protein MAB-21, and autophagy) do not have a major role in nematode excitotoxicity. In contrast, Pin1/PINN-1 (a DAPK interaction-partner and a peptidyl-prolyl isomerase involved in chronic neurodegenerative conditions) suppresses neurodegeneration in our excitotoxicity model.
Conclusions: Our studies highlight the prominence of DAPK and Pin1/PINN-1 as conserved mediators of cell death processes in diverse scenarios of neurodegeneration
Hubbard Model Approach to X-ray Spectroscopy
Thesis (Ph.D.)--University of Washington, 2012