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in creator/contributor: "McCurdy, C. William"

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Application of exterior complex scaling to positron-hydrogencollisions including rearrangement

The first application of an exterior complex scaling method to an atomic scattering problem with distinct rearrangement channels is reported. Calculations are performed for positron-hydrogen collisions in an s-wave model employing an electron-positron potential of V{sub 12} = -(8+(r{sub 1}-r{sub 2}){sup 2}){sup 1/2}, using the time-independent propagating exterior complex scaling (PECS) method. This potential has the correct long-range Coulomb tail of the full problem and the results demonstrat… more

Date: December 6, 2007

Creator: Bartlett, Philip L.; Stelbovics, Andris T.; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Implementation of exterior complex scaling in B-splines to solve atomic and molecular collision problems

B-spline methods are now well established as widely applicable tools for the evaluation of atomic and molecular continuum states. The mathematical technique of exterior complex scaling has been shown, in a variety of other implementations, to be a powerful method with which to solve atomic and molecular scattering problems, because it allows the correct imposition of continuum boundary conditions without their explicit analytic application. In this paper, an implementation of exterior complex s… more

Date: November 18, 2003

Creator: McCurdy, C. William & Martin, Fernando

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Double Photoionization of Aligned Molecular Hydrogen

We present converged, completely ab initio calculations ofthe triple differential cross sections for double photoionization ofaligned H2 molecules for a photon energy of 75.0 eV. The method ofexterior complex scaling, implemented with both the discrete variablerepresentation and B-splines, is used to solve the Schroedinger equationfor a correlated continuum wave function corresponding to a single photonhaving been absorbed by a correlated initial state. Results for a fixedinternuclear distance … more

Date: July 21, 2006

Creator: Vanroose, Wim; Horner, Daniel A.; Martin, Fernando; Rescigno,Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Progress in the Application of Classical S-Matrix Theory to Inelastic Collision Processes

Methods are described which effectively solve two of the technical difficulties associated with applying classical S‐matrix theory to inelastic/reactive scattering. Specifically, it is shown that rather standard numerical methods can be used to solve the ’’root search’’ problem (i.e., the nonlinear boundary value problem necessary to impose semiclassical quantum conditions at the beginning and the end of the classical trajectories) and also how complex classical trajectories, which are necessar… more

Date: May 1, 1980

Creator: McCurdy, C. William & Miller, William H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

New developments in the ab initio treatment of low energy electron collisions with molecules

Although there has been substantial progress in the ab initio treatment of low energy electron scattering from small diatomic and polyatomic molecules in the last few years a number of problems still remain. Most current research has focused on the calculation of fixed nuclei scattering amplitudes in the static-exchange (SE) approximation. A few calculations have gone beyond this approximation to include electron correlation and/or vibrational and rotational effects, the latter often within the… more

Date: January 1, 1989

Creator: Schneider, B. I.; Rescigno, T. N.; McCurdy, C. William & Lengsfield, Byron H., III

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Opportunities for discovery: Theory and computation in Basic Energy Sciences

New scientific frontiers, recent advances in theory, and rapid increases in computational capabilities have created compelling opportunities for theory and computation to advance the scientific mission of the Office of Basic Energy Sciences (BES). The prospects for success in the experimental programs of BES will be enhanced by pursuing these opportunities. This report makes the case for an expanded research program in theory and computation in BES. The Subcommittee on Theory and Computation of… more

Date: January 11, 2005

Creator: Harmon, Bruce; Kirby, Kate & McCurdy, C. William

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Three-body breakup in dissociative electron attachment to the water molecule

We report the results of {\em ab initio} calculations on dissociative electron attachment (DEA) to water that demonstrate the importance of including three-body breakup in the dissociation dynamics. While three-body breakup is ubiquitous in the analogous process of dissociative recombination, its importance in low-energy dissociative electron attachment to a polyatomic target has not previously been quantified. Our calculations, along with our earlier studies of DEA into two-body channels, indi… more

Date: August 28, 2008

Creator: Haxton, Daniel J.; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Triple Differential Cross sections and Nuclear Recoil in Two-Photon Double Ionization of Helium

Triple differential cross sections (TDCS) for two-photon double ionization of helium are calculated using the method of exterior complex scaling both above and below the threshold for sequential ionization (54.4 eV). It is found that sequential ionization produces characteristic behavior in the TDCS that identifies that process when it is in competition with nonsequential ionization. Moreover we see the signature in the TDCS and nuclear recoil cross sections of"virtual sequential ionizatio… more

Date: April 29, 2008

Creator: Horner, Daniel A.; McCurdy, C. William & Rescigno, Thomas N

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Cross sections for short pulse single and double ionization ofhelium

In a previous publication, procedures were proposed for unambiguously extracting amplitudes for single and double ionization from a time-dependent wavepacket by effectively propagating for an infinite time following a radiation pulse. Here we demonstrate the accuracy and utility of those methods for describing two-photon single and one-photon double ionization of helium. In particular it is shown how narrow features corresponding to autoionizing states are easily resolved with these methods.

Date: November 27, 2007

Creator: Palacios, Alicia; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Probing the nonlocal approximation to resonant collisions ofelectrons with diatomic molecules

A numerically solvable two-dimensional model introduced bythe authors [Phys. Rev. A 73, 032721 (2006)]is used to investigate thevalidity of the nonlocal approximation to the dynamics of resonantcollisions of electrons with diatomic molecules. The nonlocalapproximation to this model is derived in detail, all underlyingassumptions are specified and explicit expressions for the resonant andnon-resonant (background) T matrix for the studied processes are given.Different choices of the so-called dis… more

Date: September 7, 2007

Creator: Houfek, Karel; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Double Photoionization of excited Lithium and Beryllium

We present total, energy-sharing and triple differential cross sections for one-photon, double ionization of lithium and beryllium starting from aligned, excited P states. We employ a recently developed hybrid atomic orbital/ numerical grid method based on the finite-element discrete-variable representation and exterior complex scaling. Comparisons with calculated results for the ground-state atoms, as well as analogous results for ground-state and excited helium, serve to highlight important … more

Date: May 20, 2010

Creator: Yip, Frank L.; McCurdy, C. William & Rescigno, Thomas N.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Hybrid Orbital and Numerical Grid Representationfor Electronic Continuum Processes: Double Photoionization of Atomic Beryllium

A general approach for ab initio calculations of electronic continuum processes is described in which the many-electron wave function is expanded using a combination of orbitals at short range and the finite-element discrete variable representation(FEM-DVR) at larger distances. The orbital portion of the basis allows the efficient construction of many-electron configurations in which some of the electrons are bound, but because the orbitals are constructed from an underlying FEM-DVR grid, the c… more

Date: April 19, 2010

Creator: Yip, Frank L; McCurdy, C. William & Rescigno, Thomas N

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Nuclear Recoil Cross Sections from Time-dependent Studies of Two-Photon Double Ionization of Helium

We examine the sensitivity of nuclear recoil cross sections produced by two-photon double ionization of helium to the underlying triple differential cross sections (TDCS) used in their computation. We show that this sensitivity is greatest in the energy region just below the threshold for sequential double ionization. Accurate TDCS, extracted from non-perturbative solutions of the time-dependent Schroedinger equation, are used here in new computations of the nuclear recoil cross section.

Date: December 21, 2009

Creator: Horner, Daniel A.; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Dissociative electron attachment to the H2O molecule II: nucleardynamics on coupled electronic surfaces within the local complexpotential model

We report the results of a first-principles study of dissociative electron attachment (DEA) to H{sub 2}O. The cross sections were obtained from nuclear dynamics calculations carried out in full dimensionality within the local complex potential model by using the multi-configuration time-dependent Hartree method. The calculations employ our previously obtained global, complex-valued, potential energy surfaces for the three ({sup 2}B{sub 1}, {sup 2}A{sub 1}, and {sup 2}B{sub 2}) electronic Feshba… more

Date: December 21, 2006

Creator: Haxton, Daniel J.; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Decoding sequential vs non-sequential two-photon double ionizationof helium using nuclear recoil

Above 54.4 eV, two-photon double ionization of helium isdominated by a sequential absorption process, producing characteristicbehavior in the single and triple differential cross sections. We showthat the signature of this process is visible in the nuclear recoil crosssection, integrated over all energy sharings of the ejected electrons,even below the threshold for the sequential process. Since nuclear recoilmomentum imaging does not require coincident photoelectron measurement,the predicted im… more

Date: January 7, 2008

Creator: Horner, Daniel A.; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Explanation of observed interference patterns in the differential cross section for double photoionization of H2

We present the results of numerical calculations on the single photon double photoionization of H{sub 2} for energies between 130 eV and 240 eV. We find that our results are in excellent agreement with experimental observations. However, our interpretation of the observed interference pattern at these energies is that it is due to mixing of parallel and perpendicular components through circularly polarized light rather than due to classical double slit diffraction.

Date: January 1, 2009

Creator: Horner, Daniel A; Miyabe, Shungo; Morales, Felipe; Martin, Fernando; Rescigno, Thomas N & Mccurdy, C William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Complete Photo-Induced Breakup of the H2 Molecule as a Probe ofMolecular Electron Correlation

Despite decades of progress in quantum mechanics, electron correlation effects are still only partially understood. Experiments in which both electrons are ejected from an oriented hydrogen molecule by absorption of a single photon have recently demonstrated a puzzling phenomenon: The ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as they vibrate in their ground state. Here we report a complete numerical solution of the Schrodinger equation for… more

Date: November 17, 2005

Creator: Vanroose, Wim; Martin, Fernando; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Theoretical treatment of double photoionization of helium using a B-spline implementation of exterior complex scaling

Calculations of absolute triple differential and single differential cross sections for helium double photoionization are performed using an implementation of exterior complex scaling in B-splines. Results for cross sections, well-converged in partial waves, are presented and compared with both experiment and earlier theoretical calculations. These calculations establish the practicality and effectiveness of the complex B-spline approach to calculations of double ionization of atomic and molecu… more

Date: February 19, 2004

Creator: McCurdy, C. William; Horner, Daniel A.; Rescigno, Thomas N. & Martin, Fernando

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Two-photon double ionization of H2 at 30 eV using Exterior Complex Scaling

Calculations of fully differential cross sections for two-photon double ionization of the hydrogen molecule with photons of 30 eV are reported. The results have been obtained by using the method of exterior complex scaling, which allows one to construct essentially exact wave functions that describe thedouble continuum on a large, but finite, volume. The calculated cross sections are compared with those previously obtained by Colgan et al., and discrepancies are found for specific molecular ori… more

Date: January 20, 2009

Creator: Morales, Felipe; Martin, Fernando; Horner, Daniel; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A hybridGaussian-discrete variable representation approach to molecular continuum processes II: application to photoionization of diatomic Li2+

We describe an approach for studying molecular photoionization with a hybrid basis that combines the functionality of analytic basis sets to represent electronic coordinates near the nuclei of a molecule with numerically-defined grid-based functions. We discuss the evaluation of the various classes of two-electron integrals that occur in a hybrid basis consisting of Gaussian type orbitals (GTOs) and discrete variable representation (DVR) functions. This combined basis is applied to calculate si… more

Date: August 1, 2008

Creator: Rescigno, Thomas N; Yip, Frank L.; McCurdy, C. William & Rescigno, Thomas N.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Two-photon double ionization of the helium atom by ultrashort pulses

Two-photon double ionization of the helium atom was the subject of early experiments at FLASH and will be the subject of future benchmark measurements of the associated electron angular and energy distributions. As the photon energy of a single femtosecond pulse is raised from the threshold for two-photon double ionization at 39.5 eV to beyond the sequential ionization threshold at 54.4 eV, the electron ejection dynamics change from the highly correlated motion associated with nonsequential abs… more

Date: May 14, 2010

Creator: Palacios, Alicia; Horner, Daniel A.; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Long-time solution of the time-dependent Schroedinger equation for an atom in an electromagnetic field using complex coordinate contours

We demonstrate that exterior complex scaling (ECS) can be used to impose outgoing wave boundary conditions exactly on solutions of the time-dependent Schrodinger equation for atoms in intense electromagnetic pulses using finite grid methods. The procedure is formally exact when applied in the appropriate gauge and is demonstrated in a calculation of high harmonic generation in which multiphoton resonances are seen for long pulse durations. However, we also demonstrate that while the applic… more

Date: September 8, 2009

Creator: Tao, Liang; Vanroose, Wim; Reps, Brian; Rescigno, Thomas N. & McCurdy, C. William

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Current status and future perspectives of electron interactions with molecules, clusters, surfaces, and interfaces [Workshop on Fundamental challenges in electron-driven chemistry; Workshop on Electron-driven processes: Scientific challenges and technological opportunities]

This report is based largely on presentations and discussions at two workshops and contributions from workshop participants. The workshop on Fundamental Challenges in Electron-Driven Chemistry was held in Berkeley, October 9-10, 1998, and addressed questions regarding theory, computation, and simulation. The workshop on Electron-Driven Processes: Scientific Challenges and Technological Opportunities was held at Stevens Institute of Technology, March 16-17, 2000, and focused largely on experimen… more

Date: September 1, 2000

Creator: Becker, Kurt H.; McCurdy, C. William; Orlando, Thomas M. & Rescigno, Thomas N.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Theory and modeling in nanoscience: Report of the May 10-11, 2002 Workshop

On May 10 and 11, 2002, a workshop entitled ''Theory and Modeling in Nanoscience'' was held in San Francisco, California, sponsored by the offices of Basic Energy Science and Advanced Scientific Computing Research of the Department of Energy. The Basic Energy Sciences Advisory Committee and the Advanced Scientific Computing Advisory Committee convened the workshop to identify challenges and opportunities for theory, modeling, and simulation in nanoscience and nanotechnology, and additionally to… more

Date: June 28, 2002

Creator: McCurdy, C. William; Stechel, Ellen; Cummings, Peter; Hendrickson, Bruce & Keyes, David

Item Type: Report

Partner: UNT Libraries Government Documents Department