ASC Image

Atomistic Simulation Centre (ASC)

Modelling Matter at the Atomic Scale

School of Mathematics and Physics, Queen's University Belfast

QUB Image
Home | Research Themes | Computer Packages Members | Opportunities | Publications | Preprints | Contact | Internal

Daniel Dundas

Lecturer in Applied Mathematics and Theoretical Physics

Address

Room A7
Atomistic Simulation Centre
Department of Physics and Astronomy
School of Mathematics and Physics
Queen's University Belfast
University Road
Belfast BT7 1NN
Northern Ireland

Tel: +44 (0) 28 9097 3369
Fax: +44 (0) 28 9097 3110
Email: d.dundas@qub.ac.uk

Teaching

  1. AMA2005: Fluid Mechanics
  2. AMA4006: Practical Methods for Partial Differential Equations

Research

  1. Ultra-fast electron and photon driven dynamics in molecular systems

    The interaction of molecular systems with ultra short laser pulses provide fundamental examples of complex quantum many body systems driven far from equilibrium. A highly non perturbative and non adiabatic coupling exists between electronic and nuclear degrees of freedom which induces both charge and energy flow within the molecule. These charge and energy transfer processes occur on the femtosecond timescale, and are of extreme importance in the design of electronic devices, probes and sensors, and in the areas of condensed matter and plasma physics, medicine and biochemistry. The development of non adiabatic quantum approaches is therefore one of the great challenges in Physics. The challenge comes about through the diversity of time scales that occur in the problem. These time scales range from a few femtosecond for electron transfer through tens of femtoseconds for excitation processes to hundreds of femtoseconds characterizing the ionic motion. All these processes need to be described within a consistent dynamical picture.

    We have developed a number of approaches for describing the inteaction of molecules using both full quantum descriptions of electron and ions for small molecules and mixed, quantum classical approaches for large molecules.

    • Quantum electron-ion dynamics of small molecules

      For one- and two-electron diatomic molecules such as H2+ and H2 we can treat both the electronic and vibrational degrees of freedom exactly through the solution of the time-dependent Schroedinger equation (TDSE), assuming that the laser light is linearly polarised along the intermolecular axis. Studying such systems interacting with ultrashort intense laser pulse allows us to gain an understanding of the fundamental roles of electron-electron and electron-ion interactions in ultrafast processes and can act as a benchmark for high-precision laboratory experiment.

      We have developed computer codes based on a mixed Lagrange mesh and finite difference approach for solving the TDSE for these molecules. These include a code called THeREMIN (vibraTing HydRogEn Molecular IoN) for describing H2+ and a code called H2MOL for describing H2.

      This work is being carried out with Alejandro de la Calle.

      Pre-ionization dynamics of H2+ by an ultrashort laser pulse
      Dissociation of H2+ by a 6-cycle linearly polarized Ti:sapphire laser pulse. The molecule lies along the z-axis with the laser polarization aligned along this axis. The TDSE is solved in cylindrical coordinates with -150 ≤ z ≤ 150, 0 ≤ ρ ≤ 100, 0 ≤ R ≤ 20. In the plot the ρ coordiante has been integrated over and we focus on that part of the grid neat the atoms. We see electron wavepacket responding in antiphase to the field with very little ionization occuring. After the pulse has finished, we see wavepackets moving out in R which is indicative of dissociation.

      Relevant Papers

      1. Title: Dissociative ionization of molecules in intense laser fields

        Author(s): Dundas D., Meharg K.J., McCann J.F., Taylor K.T.

        European Physical Journal D, 26, No. 1, pp. 51-57 (OCT 2003)

      2. Title: Efficient grid treatment of the ionization dynamics of laser-driven H-2(+)

        Author(s): Dundas D.

        Physical Review A, 65, No. 2, Art. No. 023408 (FEB 2002)

    • Quantum-classical dynamics of large molecules

      The basis of this research is a time dependent density functional theory approach implemented in a real space, massively parallel computer code called EDAMAME (Ehrenfest DynAMics on Adaptive MEshes). This code was developed in both the ASC and CTAMOP.

      The aim of this research is to develop an experimental and theoretical capability that will lead to a novel method for peptide sequencing using ultrashort laser pulses. This work is being carried out with Abi Wardlow, in collaboration with Dr Jason Greenwood of the Centre for Plasma Physics at QUB.

      Ionization of Benzene by an intense, ultrashort laser pulse
      Ionization of benzene by a 5-cycle Ti:sapphire laser pulse. The benzene molecule lies in the plane and the laser pulse is linearly-polarised with the polarization direction horizontal in the plane. The laser wavelength is λ = 780 nm and its peak intensity is I = 4.0x1014 W/cm2. Ionizing electron wavepacket is emitted each half-cycle, in anti-phase to the field, as the laser electric field strength passes through maxima and minima.

    • Relevant Papers

      1. Title: Multielectron effects in high harmonic generation in N2 and benzene: Simulation using a non-adiabatic quantum molecular dynamics approach for laser-molecule interactions

        Author(s): Dundas D.

        Journal of Chemical Physics, 136, No. 19, pp. 194303-1-194303-17 (MAY 2012)

      2. Title: Molecular effects in the ionization of N2, O2, and F2 by intense laser fields

        Author(s): Dundas D., Rost J.-M.

        Physical Review A, 71, No. 1, Art. No. 013421 (JAN 2005)

  2. Non-conservative current-induced forces in nanoscale devices

    We work on the real-time simulation of current flow in these systems, and of the dynamics of the atoms driven by the huge current densities possible in atomic wires. A recent breakthrough was to prove theoretically that the forces on atoms that current flow exerts are non-conservative, and to simulate the resultant operation of a one-atom 'waterwheel'. This work was featured in two News and Views articles in the Nature Journals and sparked off experimental and theoretical interest internationally.

    Atomic waterwheels
    An open-boundary non-adiabatic molecular dynamics simulation of the corner atom in a bent atomic wire. The current in the wire is in the region of 70 μ A. The atom is driven in an expanding orbit by the non-conservative current-induced force on it. Its kinetic energy grows exponentially in time, till other factors kick in to slow it down.

    Relevant Papers

    1. Title: Current-driven atomic waterwheels

      Author(s): Dundas D., McEniry E.J., Todorov T.N.

      Nature Nanotechnology, 4, No. 2, pp. 99-102 (2009)

    2. Title: An ignition key for atomic-scale engines

      Author(s): Dundas D., Cunningham B., Buchanan C., Terasawa A., Anthony T Paxton A.T., Todorov T.N.

      Journal of Physics: Condensed Matter, 24, pp. 402203-1-402203-6 (2012)

    This work is being carried out with Tchavdar Todorov, Asako Terasawa and Brian Cunningham.