Fall 2017 Seminars
|August 28, 2017||Methods for cyclic coating test protocol development||Aaron Feickert|
|September 4, 2017|
|September 11, 2017||Molecular Dynamics Lattice Gas: a New Tool to Understand Lattice Gases and Lattice Boltzmann||Alexander Wagner|
|September 18, 2017||Differential Capacitance of Ionic Liquids with and without Added Solvent||Sylvio May|
|September 25, 2017||Probing student reasoning approaches through the lens of dual-process theories||Cody Gette|
|October 2, 2017||Lattice Gas with a Molecular Dynamics collision operator||Reza Parsa|
|October 9, 2017||Rejection-free cluster Monte Carlo algorithms in the presence of symmetry-breaking fields||Yen Lee Loh|
|October 16, 2017|
|October 27, 2017||<special day>Electrostatic Interactions at Dielectric Interfaces: From Membranes to Colloids||Guilherme Bossa|
|October 30, 2017||Superintegrability in classical and quantum mechanics||Bjorn Berntson|
|November 6, 2017||Multi-functional liquid crystalline epoxy networks||Mike Kessler|
|November 13, 2017||The Full Spectrum Boost project in nanoparticle solar cells: Downconversion, Upconversion, Transport.||Gergely Zimanyi|
|November 15, 2017||<Special Day>Entangled Granular Materials||Scott Franklin|
|November 20, 2017||Crowding in Polymer-Nanoparticle Mixtures||Wyatt Davis|
|November 27, 2017||The role of adhesion in crumpled polymer films||Andrew Croll|
|December 4, 2017||Carrier Multiplication in Chiral Single-Walled Carbon Nanotubes and Silicon Nanowires: DFT-Based Study||Deyan Mihaylov|
|December 11, 2017||<Final Exam Week>|
Carrier Multiplication in Chiral Single-Walled Carbon Nanotubes and Silicon Nanowires: DFT-Based Study
Department of Physics,
North Dakota State University
Monday December 4, 3:00-4:00pm,
221 South Engineering
The conclusion about multiple exciton generation (MEG) efficiency in a nanoparticle can only be made by comprehensive study of different relaxation channels, such as phonon-mediated carrier thermalization, carrier multiplication and recombination, etc. Here, we study time evolution of a photo-excited state using Boltzmann transport equation (BE) that includes phonon emission/absorption together with the exciton multiplication and recombination. BE rates are computed using non-equilibrium finite-temperature many-body perturbation theory (MBPT) based on DFT simulations. Exciton effects are included by solving Bethe-Salpeter equation with RPA-screened Coulomb interaction (with additional simplifying approximations). We compute rates for both all-singlet MEG and Singlet Fission channels, which are of order 1014 s-1. For all-singlet MEG we calculate internal quantum efficiency (QE), the number of excitons generated from a single absorbed photon. Efficient MEG in chiral single-wall carbon nanotubes (SWCNTs), such as (6,2), both pristine and Cl-doped, and (6,5) is present within the solar spectrum range. We predict QE = 1.3-1.6 at the excitation energy of 3 times the optical gap in (6,2) and (6,5). However, QE = 1 is found in CNT (10,5) which suggests strong chirality dependence of MEG. MEG efficiency in functionalized SWCNTs is enhanced compared to the pristine case. Also, we calculate corrections to the bi-exciton state energy due to exciton-exciton interactions.
Theory and simulation of dispersions with competing interactions applied to protein solutions
Institute of Complex Systems (ICS-3),
Forschungszentrum Jülich GmbH
Monday February 12, 3:00-4:00pm,
221 South Engineering
Dynamic clustering of globular particles in dispersions exhibiting competing short-range attraction and long-range repulsion (SALR) such as in low-salinity protein solutions has gained a lot of interest over the past years. We investigate the influence of clustering on the dynamics and structure of globular particle dispersions. For this purpose, we combine a semianalytic hybrid method where hydrodynamic interactions (HIs) are approximately included  with multi-particle collision (MPC) simulations accounting for the full many-particles HIs . By this simulation-theory comparison, we establish the high accuracy of the hybrid method for calculating diffusion and viscosity properties of SALR systems in the dispersed fluid phase region. We show that a cluster peak is present also in the hydrodynamic function characterizing the short-time dynamics, in accord with neutron spin echo results on lysozyme solutions . Enhanced short-range attraction leads to a smaller self-diffusion coefficient and a larger dispersion viscosity. The behavior of the (generalized) sedimentation coefficient is more intricate showing, e.g., non-monotonic interaction strength dependence. Inter- and intraclusters dynamics in the equilibrium cluster phase region is analyzed using MPC simulations . Simulation results for the mean cluster lifetime, and the comparison with the dissociation time of an isolated particle pair reveal quantitative differences, pointing to the importance of many-particle HIs for the cluster dynamics. The cluster lifetime in the cluster-fluid phase increases far stronger with increasing attraction strength than in the dispersed-fluid phase. Significant changes in cluster shapes are observed in the course of time.
 J. Riest and G. Nägele, Short-time dynamics in dispersions with competing short-range attraction and long-range repulsion, Soft Matter 11, 9273 (2015).
 S. Das, J. Riest, R.G. Winkler, G. Gompper, J.K.G. Dhont and G. Nägele, Clustering and dynamics of particles in dispersions with competing interaction: Theory and simulation, submitted (2017).
 J. Riest, G. Nägele, N.J. Wagner, Y. Liu (NIST), and D. Godfrin, Short-time dynamics of Lysozyme solutions with competing short-range attraction and long-range repulsion: Experiment and theory, submitted (2017).
Methods for calculating effective interactions and pressure in charge-stabilized dispersions with application to filtration
Candidate for Ph.D.,
Institute of Complex Systems
Forschungszentrum Jülich GmbH
<Special Day>Tuesday February 13, Time TBA,
221 South Engineering
Charge-stabilized suspensions have interesting static features, reflected in properties such as the suspension osmotic pressure and ionic microstructure. These properties are determined by electro-steric interactions between all ionic species. Due to the large size asymmetry between colloidal macroions and small microions, the degrees of freedom of the latter can be integrated out, resulting in an effective one-component interaction potential describing microion-dressed colloidal quasi-particles.
We present a comparison, and partial extension, of various methods of calculating effective colloidal interaction parameters including effective charges and screening constants as functions of concentration and ionic strength . We discuss osmotic suspension pressure calculations for dispersions in Donnan equilibrium with a salt ion reservoir. Methods are discussed including cell-models, renormalized jellium models, and multi-colloid-centered mean-field models. The pros and cons of the various methods are assessed by comparison with primitive model based computer simulations.
As an application to a technologically relevant process, a parameter-free model for cross-flow ultrafiltration is presented . In this process, a dilute charge-stabilized dispersion is concentrated and purefied by continouosly pumping it though an array of cylindrical membranes having nano-sized pores.
 M. Brito, J. Riest, A. Denton and G. Nägele, to be submitted (2017).
 M. Brito, J. Riest, O. Nir, M. Wessling and G. Nägele, work in progress.
Spring 2018 Seminars
|Jan 8, 2018||<TBA>||Timothy Twohig|
|Jan 15, 2018|
<Martin Luther King, Jr. Day>
|January 22, 2018|
|January 29, 2018||<TBA>||Alan Denton|
|February 5, 2018|
|February 12, 2018||Theory and simulation of dispersions with competing interactions applied to protein solutions||Gerhard Nägele|
|February 13, 2018||Methods for calculating effective interactions and pressure in charge-stabilized dispersions with application to filtration||Mariano Brito|
|February 19, 2018||<President's Day>|
|February 26, 2018||Time-Dependent Excited State Molecular Dynamics: from photo-fragmentation to photo-polymerization||Yulun Han|
|March 5, 2018||<APS March Meeting>|
|March 12, 2018||<Spring Break>|
|March 19, 2018|
|March 26, 2018|
|April 2, 2018||<Holiday>|
|April 9, 2018|
|April 16, 2018|
|April 23, 2018|
|April 30, 2018|
|May 7, 2018||<Final Exam Week>|
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