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Molecular Dynamics

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Full-Text Articles in Physics

A Molecular Dynamics Study Of Temperature Dependent Wetting In Alkane-Water Systems, Pauf Neupane Jan 2020

A Molecular Dynamics Study Of Temperature Dependent Wetting In Alkane-Water Systems, Pauf Neupane

Doctoral Dissertations

“The wetting behavior of aqueous organic systems is of great importance in several environmental and industrial processes such as the formation and growth of atmospheric aerosols, crude oil recovery from an oil field, onsite cleaning of natural gas, and clean-up of oil spills. In this work, we employed molecular dynamics (MD) simulations to explore the temperature dependent wetting behavior of octane and nonane on water in planar interfaces as well as in nanodroplets using PYS alkane and SPC/E and TIP4P/2005 water models.

For planar interfaces, we found unusual wetting behavior of octane and nonane on SPC/E water ...


Phase Diagram Of Nuclear Matter, Adrian Gaytan Terrazas Jan 2019

Phase Diagram Of Nuclear Matter, Adrian Gaytan Terrazas

Open Access Theses & Dissertations

Nowadays it is well known that nuclear matter has a liquid and a gas phase, as well as a coexistence of phases region. Symmetric nuclear matter (same number of protons and neutrons) exhibit phase transitions from the gas phase to a liquid-gas mixture. A useful tool to represent such phases and transitions is through diagrams that show the necessary conditions of density and temperature to be in either of the phases.

Now the question is, what if we extend the traditional phase diagram for symmetric matter to the asymmetric

cases (different number of protons and neutrons)?

This study uses classical ...


The Structural Information Filtered Features Potential For Machine Learning Calculations Of Energies And Forces Of Atomic Systems., Jorge Arturo Hernandez Zeledon Jan 2019

The Structural Information Filtered Features Potential For Machine Learning Calculations Of Energies And Forces Of Atomic Systems., Jorge Arturo Hernandez Zeledon

Graduate Theses, Dissertations, and Problem Reports

In the last ten years, machine learning potentials have been successfully applied to the study of crystals, and molecules. However, more complex materials like clusters, macro-molecules, and glasses are out reach of current methods. The input of any machine learning system is a tensor of features (the most universal type are rank 1 tensors or vectors of features), the quality of any machine learning system is directly related to how well the feature space describes the original physical system. So far, the feature engineering process for machine learning potentials can not describe complex material. The current methods are highly inefficient ...


Theory Of Collisional Transport In Ultracold Neutral Plasmas, Nathaniel R Shaffer Dec 2018

Theory Of Collisional Transport In Ultracold Neutral Plasmas, Nathaniel R Shaffer

Theses and Dissertations

Ultracold neutral plasmas (UNP) are laboratory plasmas formed by the photoionization of a magneto-optically trapped and cooled gas. Because of their unusually low temperatures, UNPs are an example of a strongly coupled plasma, meaning that the potential energy of Coulomb interactions between particles is comparable to or greater than their thermal kinetic energy. In the field of strongly coupled plasmas, which also includes dense plasmas found in astrophysics and inertial confinement fusion experiments, there is a pressing need to better understand the collisional transport of matter, momentum, and energy between electrons and ions. The main result of this thesis is ...


Understanding The Nature Of Nanoscale Wetting Through All-Atom Simulations, Oliver Evans Jan 2018

Understanding The Nature Of Nanoscale Wetting Through All-Atom Simulations, Oliver Evans

Williams Honors College, Honors Research Projects

The spreading behavior of spherical and cylindrical water droplets between 30Å and 100Å in radius on a sapphire surface is investigated using all-atom molecular dynamics simulations for durations on the order of tens of nanoseconds. A monolayer film develops rapidly and wets the surface, while the bulk of the droplet spreads on top of the monolayer, maintaining the shape of a spherical cap. Unlike previous simulations in the literature, the bulk radius is found to increase to a maximum value and receed as the monolayer continues to expand. Simple time and droplet size dependence is observed for monolayer radius and ...


Dynamics Of Discs In A Nematic Liquid Crystal, Alena Antipova May 2016

Dynamics Of Discs In A Nematic Liquid Crystal, Alena Antipova

Electronic Thesis and Dissertation Repository

In this thesis, a new way of simulating a two-way coupling between a liquid crystal and an immersed object is proposed. It can be used for objects of various geometries and can be expanded to be used for an object of any geometry. Additionally, a simple yet effective model was suggested for calculations of transmitted light through a nematic liquid crystal sample. This model allowed us to clarify the behavior of a ferromagnetic disc in a nematic liquid crystal observed in experiments and incorrectly interpreted at that time.

Our simulations have demonstrated the following: in the absence of external forces ...


Molecular Dynamics Study On Defect Reduction Strategies Towards The Fabrication Of High Performance Cd1-Xznxte/Cds Solar Cells, Jose Juan Chavez Jan 2015

Molecular Dynamics Study On Defect Reduction Strategies Towards The Fabrication Of High Performance Cd1-Xznxte/Cds Solar Cells, Jose Juan Chavez

Open Access Theses & Dissertations

Cadmium Telluride is a material widely used in terrestrial thin film photovoltaic applications due to its nearly ideal band gap (~1.5 eV) and high absorption coefficient. Due to its low manufacturing cost, this technology has the potential to become a significant energy resource if higher energy conversion efficiencies are achieved. However, the module efficiencies (~14%) are still far from the theoretical maximum (~30%) for this material in a single junction configuration. The reason behind this low performance is attributed to the high number of defects that are present within the device materials. The physics behind the formation mechanisms of ...


Building Predictive Chemistry Models, Christopher Browne, Nicolas Onofrio, Alejandro Strachan Aug 2014

Building Predictive Chemistry Models, Christopher Browne, Nicolas Onofrio, Alejandro Strachan

The Summer Undergraduate Research Fellowship (SURF) Symposium

Density Functional Theory (DFT) simulations allow for sophisticated modeling of chemical interactions, but the extreme computational cost makes it inviable for large scale applications. Molecular dynamics models, specifically ReaxFF, can model much larger simulations with greater speed, but with lesser accuracy. The accuracy of ReaxFF can be improved by comparing predictions of both methods and tuning ReaxFF’s parameters. Molecular capabilities of ReaxFF were gauged by simulating copper complexes in water over a 200 ps range, and comparing energy predictions against ReaxFF. To gauge solid state capabilities, volumetric strain was applied to simulated copper bulk and the strain response functions ...


Kapitza Resistance Of Si/Sio₂ Interface, Bowen Deng, Aleksandr V. Chernatynskiy, Marat Khafizov, David H. Hurley, Simon R. Phillpot Jan 2014

Kapitza Resistance Of Si/Sio₂ Interface, Bowen Deng, Aleksandr V. Chernatynskiy, Marat Khafizov, David H. Hurley, Simon R. Phillpot

Physics Faculty Research & Creative Works

A phonon wave packet dynamics method is used to characterize the Kapitza resistance of a Si/SiO2 interface in a Si/SiO2/Si heterostructure. By varying the thickness of SiO2 layer sandwiched between two Si layers, we determine the Kapitza resistance for the Si/SiO 2 interface from both wave packet dynamics and a direct, non-equilibrium molecular dynamics approach. The good agreement between the two methods indicates that they have each captured the anharmonic phonon scatterings at the interface. Moreover, detailed analysis provides insights as to how individual phonon mode scatters at the interface and their contribution ...


Phonon Thermal Transport Through Tilt Grain Boundaries In Strontium Titanate, Zexi Zheng, Xiang Chen, Bowen Deng, Aleksandr V. Chernatynskiy, Shengfeng Yang, Jinjun Xiong, Youping Chen Jan 2014

Phonon Thermal Transport Through Tilt Grain Boundaries In Strontium Titanate, Zexi Zheng, Xiang Chen, Bowen Deng, Aleksandr V. Chernatynskiy, Shengfeng Yang, Jinjun Xiong, Youping Chen

Physics Faculty Research & Creative Works

In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO3. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO3 contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance ...


Hybrid Lattice Boltzmann - Molecular Dynamics Simulations With Both Simple And Complex Fluids, Frances E. Mackay Apr 2013

Hybrid Lattice Boltzmann - Molecular Dynamics Simulations With Both Simple And Complex Fluids, Frances E. Mackay

Electronic Thesis and Dissertation Repository

The behaviour and properties of colloidal suspensions strongly depend on the interactions arising between the immersed colloidal particles and the solvent. However, modelling such interactions is not at all straightforward; the larger time and length scales experienced by the colloidal particles compared to the solvent molecules makes all-atom molecular dynamics (MD) simulations of such systems completely impractical. Therefore a coarse-grained representation of the fluid is required, along with a method to couple this fluid to the colloidal particles.

In the first part of this thesis, we propose a new method for coupling both point and composite MD particles to an ...


Non-Equilibrium Melting And Sublimation Of Graphene Simulated With Two Interatomic Potentials, Brad Steele Jan 2013

Non-Equilibrium Melting And Sublimation Of Graphene Simulated With Two Interatomic Potentials, Brad Steele

Graduate Theses and Dissertations

The mechanisms of the sublimation of graphene at zero pressure and the condensation of carbon vapor is investigated by molecular dynamics (MD) simulations. The interatomic interactions are described by the Reactive Empirical Bond Order potential (REBO). It is found that graphene sublimates at a temperature of 5,200 K. At the onset of sublimation, defects that contain several pentagons and heptagons are formed, that are shown to evolve from double vacancies and stone wales defects. These defects consisting of pentagons and heptagons act as nucleation sites for the gaseous phase. The influence of the interatomic interactions on the sublimation process ...


Development Of Interatomic Potentials For Large Scale Molecular Dynamics Simulations Of Carbon Materials Under Extreme Conditions, Romain Perriot Jan 2012

Development Of Interatomic Potentials For Large Scale Molecular Dynamics Simulations Of Carbon Materials Under Extreme Conditions, Romain Perriot

Graduate Theses and Dissertations

The goal of this PhD research project is to devise a robust interatomic potential for large scale molecular dynamics simulations of carbon materials under extreme conditions. This screened-environment dependent reactive empirical bond order potential (SED-REBO) is specifically designed to describe carbon materials under extreme compressive or tensile stresses. Based on the original REBO potential by Brenner and co workers, SED-REBO includes reparametrized pairwise interaction terms and a new screening term, which serves the role of a variable cutoff. The SED-REBO potential overcomes the deficiencies found with the most commonly used interatomic potentials for carbon: the appearance of artificial forces due ...


Properties Of Ferroelectric Perovskite Structures Under Non-Equilibrium Conditions, Qingteng Zhang Jan 2012

Properties Of Ferroelectric Perovskite Structures Under Non-Equilibrium Conditions, Qingteng Zhang

Graduate Theses and Dissertations

Ferroelectric materials have received lots of attention thanks to their intriguing properties such as the piezoelectric and pyroelectric effects, as well as the large dielectric constants and the spontaneous polarization which can potentially be used for information storage. In particular, perovskite crystal has a very simple unit cell structure yet a very rich phase transition diagram, which makes it one of the most intensively studied ferroelectric materials. In this dissertation, we use effective Hamiltonian, a first-principles-based computational technique to study the finite-temperature properties of ferroelectric perovskites. We studied temperature-graded

(BaxSr1-x )TiO3 (BST) bulk alloys as well as the dynamics of ...


Atomistic Studies Of Shock-Wave And Detonation Phenomena In Energetic Materials, Mikalai Budzevich Jan 2011

Atomistic Studies Of Shock-Wave And Detonation Phenomena In Energetic Materials, Mikalai Budzevich

Graduate Theses and Dissertations

The major goal of this PhD project is to investigate the fundamental properties of energetic materials, including their atomic and electronic structures, as well as mechanical properties, and relate these to the fundamental mechanisms of shock wave and detonation propagation using state-of-the-art simulation methods. The first part of this PhD project was aimed at the investigation of static properties of energetic materials (EMs) with specific focus on 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). The major goal was to calculate the isotropic and anisotropic equations of state for TATB within a range of compressions not accessible to experiment, and to make ...


Structural, Electronic, Vibrational And Thermodynamical Properties Of Surfaces And Nanoparticles, Handan Yildirim Jan 2010

Structural, Electronic, Vibrational And Thermodynamical Properties Of Surfaces And Nanoparticles, Handan Yildirim

Electronic Theses and Dissertations, 2004-2019

The main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the 'bottom-up' approach for which the knowledge gathered at the scale of atoms and NPs serves as a base to build, at the macroscopic scale, materials with desired physical and chemical properties. We use a ...


Simulation And Analysis Of Cadmium Sulfide Nanoparticles, Chad Everett Junkermeier Dec 2008

Simulation And Analysis Of Cadmium Sulfide Nanoparticles, Chad Everett Junkermeier

Theses and Dissertations

I used ab initio molecular dynamics calculations to model cadmium sulfide nanoparticles. The nanoparticles were originaly spherical, bulk-like zinc-blende structures. Constant temperature molecular dynamics calculations reveals that CdS nanoparticles that are about 2 nm in diameter and have unpassivated surfaces are in an amorphous structure with short range order. The nearest neighbor distance on the surface of the nanoparticles being near the wurtzite nearest neighbor distance. I wrote the program xyzSTATS and used its results in justifying the amorphous nanoparticles claim. I also estimated the band gap of the CdS nanoparticles with unpassivated dangling bonds.


Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai Dec 2008

Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai

Physics Faculty Research & Creative Works

We observe high-order harmonic spectra generated from a thin atomic medium, Ar, Kr, and Xe, by intense 800-nm and 1300-nm femtosecond pulses. A clear signature of a single-atom response is observed in the harmonic spectra. Especially in the case of Ar, a Cooper minimum, reflecting the electronic structure of the atom, is observed in the harmonic spectra. We successfully extract the photorecombination cross sections of the atoms in the field-free condition with the help of an accurate recolliding electron wave packet. The present protocol paves the way for exploring ultrafast imaging of molecular dynamics with attosecond resolution.


Retrieval Of Electron-Atom Scattering Cross Sections From Laser-Induced Electron Rescattering Of Atomic Negative Ions In Intense Laser Fields, Xiaoxin Zhou, Zhangjin Chen, Toru Morishita, Anh-Thu Le, C. D. Lin May 2008

Retrieval Of Electron-Atom Scattering Cross Sections From Laser-Induced Electron Rescattering Of Atomic Negative Ions In Intense Laser Fields, Xiaoxin Zhou, Zhangjin Chen, Toru Morishita, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We investigated the two-dimensional electron momentum distributions of atomic negative ions in an intense laser field by solving the time-dependent Schrödinger equation (TDSE) and using the first- and second-order strong-field approximations (SFAs). We showed that photoelectron energy spectra and low-energy photoelectron momentum distributions predicted from SFAs are in reasonable agreement with the solutions from the TDSE. More importantly, we showed that accurate electron-atom elastic scattering cross sections can be retrieved directly from high-energy electron momentum spectra of atomic negative ions in the laser field. This opens up the possibility of measuring electron-atom and electron-molecule scattering cross sections from the photodetachment ...


Two-Loop Bethe Logarithms For Non- S Levels, Ulrich D. Jentschura Dec 2006

Two-Loop Bethe Logarithms For Non- S Levels, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

Two-loop Bethe logarithms are calculated for excited P and D states in hydrogenlike systems, and estimates are presented for all states with higher angular momenta. These results complete our knowledge of the P and D energy levels in hydrogen at the order of α8 mec2, where me is the electron mass and c is the speed of light, and scale as Z6, where Z is the nuclear charge number. Our analytic and numerical calculations are consistent with the complete absence of logarithmic terms of order (απ)2 (Zα)6 ln [(Zα)-2] mec ...


Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel Nov 2005

Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

We investigate quantum electrodynamic effects under the influence of an external, time-dependent electromagnetic field, which mediates dynamic modifications of the radiative corrections. Specifically, we consider the quantum electrodynamic vacuum-polarization tensor under the influence of two external background fields: a strong laser field and a nuclear Coulomb field. We calculate the charge and current densities induced by a nuclear Coulomb field in the presence of a laser field. We find the corresponding induced scalar and vector potentials. The induced potential, in first-order perturbation theory, leads to a correction to atomic energy levels. The external laser field breaks the rotational symmetry of ...


Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin Mar 2005

Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin

Physics Faculty Research & Creative Works

We present the positronium formation cross sections for a positron colliding with lithium and sodium for the collision energies from 0.01 eV up to 20 eV by the hyperspherical close-coupling method. For Li, our results agree with the experimental data and with other calculations. Our results for Na remain in agreement with previous close-coupling calculations, but do not support the latest experimental data for Na below 1 eV. To validate our model potentials and method in the low-energy regime, the binding energies of positronic lithium and positronic sodium as well as the s-wave scattering lengths for positronium scattering from ...


Simulation Studies Of Self-Assembly And Phase Diagram Of Amphiphilic Molecules, Geuorgui Kostadinov Bourov Jan 2005

Simulation Studies Of Self-Assembly And Phase Diagram Of Amphiphilic Molecules, Geuorgui Kostadinov Bourov

Electronic Theses and Dissertations, 2004-2019

The aim of this dissertation is to investigate self-assembled structures and the phase diagram of amphiphilic molecules of diverse geometric shapes using a number of different computer simulation methods. The semi-realistic coarse-grained model, used extensively for simulation of polymers and surfactant molecules, is adopted in an off-lattice approach to study how the geometric structure of amphiphiles affects the aggregation properties. The results of simulations show that the model system behavior is consistent with theoretical predictions, experiments and lattice simulation models. We demonstrate that by modifying the geometry of the molecules, self-assembled aggregates are altered in a way close to theoretical ...


Breakup Of H₂ In Singly Ionizing Collisions With Fast Protons: Channel-Selective Low-Energy Electron Spectra, Christina Dimopoulou, Robert Moshammer, Daniel Fischer, C. Hohr, Alexander Dorn, Pablo Daniel Fainstein, Jose R. Crespo Lopez-Urrutia, Claus Dieter Schroter, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Sep 2004

Breakup Of H₂ In Singly Ionizing Collisions With Fast Protons: Channel-Selective Low-Energy Electron Spectra, Christina Dimopoulou, Robert Moshammer, Daniel Fischer, C. Hohr, Alexander Dorn, Pablo Daniel Fainstein, Jose R. Crespo Lopez-Urrutia, Claus Dieter Schroter, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

The dissociation of H2 in singly ionizing collisions with fast protons was analyzed using channel-selective low-energy electron spectra. Dissociative and nondissociative single ionization of H2 by 6MeV proton impact was described in a kinematically by determining momentum vectors of electron and H+ fragment of H2+ target ion, respectively. The electron spectra exhibited role of autoionization of doubly and singly excited states of H2. The doubly and singly excited states of H2 involve coupling between electronic and nuclear motion of molecule.


Extrapolation Of The Zα-Expansion And Two-Loop Bound-State Energy Shifts, Ulrich D. Jentschura Jul 2003

Extrapolation Of The Zα-Expansion And Two-Loop Bound-State Energy Shifts, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

Quantum electrodynamic (QED) effects that shift the binding energies of hydrogenic energy levels have been expressed in terms of a semi-analytic expansion in powers of Zα and ln[(Zα)-2], where Z is the nuclear charge number and α is the fine-structure constant. For many QED effects, numerical data are available in the domain of high Z where the Zα expansion fails. In this Letter, we demonstrate that it is possible, within certain limits of accuracy, to extrapolate the Zα-expansion from the low-Z to the high-Z domain. We also review two-loop self-energy effects and provide an estimate for the problematic ...


Projectile-Charge Sign Dependence Of Four-Particle Dynamics In Helium Double Ionization, Daniel Fischer, Robert Moshammer, Alexander Dorn, Jose R. Crespo Lopez-Urrutia, Bernold Feuerstein, C. Hohr, Claus Dieter Schroter, Siegbert Hagmann, Holger Kollmus, Rido Mann, Bhas Bapat, Joachim Hermann Ullrich, Holger Kollmus Jun 2003

Projectile-Charge Sign Dependence Of Four-Particle Dynamics In Helium Double Ionization, Daniel Fischer, Robert Moshammer, Alexander Dorn, Jose R. Crespo Lopez-Urrutia, Bernold Feuerstein, C. Hohr, Claus Dieter Schroter, Siegbert Hagmann, Holger Kollmus, Rido Mann, Bhas Bapat, Joachim Hermann Ullrich, Holger Kollmus

Physics Faculty Research & Creative Works

Double ionization of helium by 6 MeV proton impact has been explored in a kinematically complete experiment using a “reaction microscope.” For the first time, fully differential cross sections for positively charged projectiles have been obtained and compared with data from 2 keV electron impact. The significant differences observed in the angular distribution of the ejected electrons are attributed to the charge sign of the projectile, resulting in different dynamics of the four-particle Coulomb system, which is not considered in the first Born approximation.


Molecular Dynamics Simulations Of Phase Transition In Agno3, Jianjun Liu, Chun-Gang Duan, M. M. Ossowski, Wai-Ning Mei, Robert W. Smith, J. R. Hardy Mar 2002

Molecular Dynamics Simulations Of Phase Transition In Agno3, Jianjun Liu, Chun-Gang Duan, M. M. Ossowski, Wai-Ning Mei, Robert W. Smith, J. R. Hardy

Chemistry Faculty Publications

Structural phase transition in AgNO3 at high temperature is simulated by molecular dynamics. The simulations are based on the potentials calculated from the Gordon–Kim modified electron-gas formalism extended to molecular ionic crystals. AgNO3 transforms into rhombohedral structure at high temperature and the phase transition is associated with the rotations of the NO3 ions and displacements of the NO3 and Ag ions.


Non-Sequential Double Ionization Of Ne In Intense Laser Pulses: A Coincidence Experiment, Robert Moshammer, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Joachim Hermann Ullrich, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner Mar 2001

Non-Sequential Double Ionization Of Ne In Intense Laser Pulses: A Coincidence Experiment, Robert Moshammer, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Joachim Hermann Ullrich, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner

Physics Faculty Research & Creative Works

The dynamics of Neon double ionization by 25 fs, 1.0 PW/cm2 laser pulses at 795 nm has been studied in a many particle coincidence experiment. The momentum vectors of all ejected atomic fragments (electrons and ions) have been measured using combined electron and recoil-ion momentum spectroscopy. Electron emission spectra for double and single ionization will be discussed. In both processes the mean electron energies differ considerably and high energetic electrons with energies of more than 120 eV have been observed for double ionization. The experimental results are in qualitative agreement with the rescattering model.


Molecular-Dynamics Simulations Of Some Baxf4 Compounds, John Flocken, Z. Mo, Wai-Ning Mei, John R. Hardy, Dorian Hatch Jan 1994

Molecular-Dynamics Simulations Of Some Baxf4 Compounds, John Flocken, Z. Mo, Wai-Ning Mei, John R. Hardy, Dorian Hatch

Physics Faculty Publications

We have carried out molecular-dynamics simulations on BaXF4 compounds, where X is Mg, Mn, or Zn. Ab initio potentials, with no adjustable parameters, were used to obtain short-range interactions between ion pairs. We found a polar ground-state structure which is in agreement with the A21am space group reported experimentally. We were able to reverse polarization in BaMgF4 at high temperatures, using large fields, but were unable to reverse polarization in the other compounds. The second-order phase transition in the Mn compound at 250 K was reproduced. We believe this to be the first extension of ...