Bulletin of the American Physical Society
2018 Joint Fall Meeting of the Texas Sections of APS, AAPT and Zone 13 of the SPS
Volume 63, Number 18
Friday–Saturday, October 19–20, 2018; University of Houston, Houston, Texas
Session K04: Computational/Nanoscience |
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Chair: Muhammad Maqbool, University of Alabama, Birmingham Room: Science and Engineering Classroom (SEC) 203 |
Saturday, October 20, 2018 10:00AM - 10:12AM |
K04.00001: First-principles structural studies of polythiophene isomeric systems John W Mintmire Recent experimental work has been reported for the synthesis of poly-ortho-thiophenes, in particular helical poly(5-alkyl-2,3-thiophene)s. These polythiophenes differ from the poly(3-alkyl-2,5-thiophene)s studied over for the past several decades as electroactive polymers similar to the polypyrroles, and which have had application in bulk heterojunction photovoltaics. We have carried out first-principles, density functional simulations for the electronic structure and total energy of a range of polythiophene systems using Gaussian-function-based orbitals in a band structure approach using helical symmetry. We have examined the hydrogen, methyl, ethyl, and propyl substituted poly(5-alkyl-2,3-thiophene)s and poly(3-alkyl-2,5-thiophene)s, optimizing the geometry as a function of twist angle in the helical backbone. We have also looked into other possible polymer conformations such as the poly(5-alkyl-2,4-thiophene)s. |
Saturday, October 20, 2018 10:12AM - 10:24AM |
K04.00002: First-principle Study of the TiO2 Single-walled Nanotubes for Photocatalysis Application Jiao An The geometric and electronic properties of the TiO2 single-wall nanotubes, constructed by rolling the most stable nanosheet along the (n,0) and (n,n) directions, have been investigated systematically. The strain energies of the nanotubes decrease monotonically as the radii of the nanotubes increase, regardless of the rolling direction. The band gaps of the nanotubes are increasing with the increase of the n value, approaching the value of the nanosheet. However, there is one nanotube significantly different from the others, i.e., the (6,0) nanotube. The substantial structural change of (6,0) nanotube causes a reduction of the band gap. Then, the isovalent sulfur (S) substitution and adsorption with the (6,0) nanotube have been studied. The band gaps are further reduced by 35% for S substitution and 22% for S adsorption, respectively. Aligning the band edge to that of bulk TiO2, it shows that the (6,0) nanotube with S substitution and adsorption both cover redox potentials of water splitting. |
Saturday, October 20, 2018 10:24AM - 10:36AM |
K04.00003: A Novel, Multi-scale Diffuse Interface Method for Macro-scale Multiphase Flows with Micro-scale Modeling of Phase Change Ping He It is a grand challenge to accurately model phase-change multiphase flows because of the tight coupling between thermodynamics and transport phenomena in 3D. The classical diffuse interface methods implicitly capture the phase interface, and phase change across interface, through solving the coupled equilibrium and non-equilibrium Gibbs energies. The equilibrium energy results in phase separation, while the non-equilibrium energy promotes molecular diffusion across interface. The balance of the two yields a rapid, smooth transitioning interface. However, classical methods capture a physical interfacial transition, whose thickness is extremely smaller than the scale of macro-scale problems below critical conditions. This research proposes a novel diffuse interface method through developing a new non-equilibrium Gibbs energy model, which bridges the micro-scale interfacial phenomena with the macro-scale flows. The new non-equilibrium model proposed here consists of (1) a nucleation potential originated from the phase stability computation, and (2) an averaged gradient term based on the phase equilibrium flash calculation. Our results show accurate predictions of the phase change and evolution in binary mixtures at different temperatures and pressures. |
Saturday, October 20, 2018 10:36AM - 10:48AM |
K04.00004: Calculating Relativistic Atomic and Molecular Properties Using Monte Carlo Methods Steven A Alexander, R.L. Coldwell There are a number of computational methods that can be used to calculate the energies and properties of nonrelativistic atoms and molecules. Fully relativistic calculations of these systems are much less common and more complicated. In part, this is because each relativistic particle generates four coupled components and the presence of negative energy states prohibits the use of most variational techniques. In this talk I will describe how variational Monte Carlo methods can be used to calculate the energy and properties of fully relativistic atoms and molecules. Results for both one electron and two electron systems will be presented. |
Saturday, October 20, 2018 10:48AM - 11:00AM |
K04.00005: Creating a Nanoscale Electromotor using DNA Origami Joseph K Pelletier DNA origami is a preferred method of nanostructure fabrication due to the self-assembly and predictable nanostructure of DNA. A DNA origami water wheel was designed using caDNAno software and simulated inside a solution of H2O with a 1M NaCl concentration and under a potential difference of 250 mV. Under these conditions, the DNA water wheel was not able to make a full rotation, but it proved that rotation is possible. This would be the first time a functioning nanoscale electromotor has been simulated and would be the first demonstration of the direct conversion of electric field into rotary motion in a nanoscale man-made system. In this talk, I will present the design of the DNA origami water wheel along with the inspiration behind it, how the fabrication method of DNA origami works, and future work that needs to be completed in order to create a functioning electromotor. |
Saturday, October 20, 2018 11:00AM - 11:12AM |
K04.00006: Neutron-Induced & gamma;-ray Production on Li and F Beemnet Alemayehu The Van de Graaff accelerator at the University of Kentucky Accelerator Laboratory was used to accelerate a pulsed- and bunched-proton beam (Δt ≈ 1 ns) that produced neutron through the p + 3H n + 3He reaction in a 3-cm long gas cell located at the end of the beamline. The resulting neutrons then scattered off samples of interest. The research focus was on the nuclei of lithium and fluorine atoms, which are important for energy-production applications- Angular distributions for gamma-ray emission from 19F (1348 and 1356 keV γ-rays) have been measured for several incident neutron energies ranging from 0.8 to 4.5 MeV. The experimental designs, calculations, detection techniques for emitted gamma rays and neutrons, and preliminary analysis of the data will be described. The resulting angular distributions, based on the a4 coefficients, show the excitation functions measured at 125o do not need to include the feeding factors that depend on the spin of the levels. The results from these measurements are important for determining neutron scattering cross sections for Li and F. |
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