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.

Two distinct strands of research are currently being taken forward. The basis of these strands 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.

Laser-controlled ionization and fragmentation of biomolecules
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 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.

Laser-controlled current flow in molecular scale devices
The aim of this research is to understand how molecular devices function in the presence of transient currents and to use this knowledge to fabricate devices in which current flow can be controlled on ultrafast timescales. Such knowledge is crucial for application to realistic devices since, at the most basic level, current switching will be required. This work has direct connections to the transport work carried out in the ASC as it will combine EDAMAME with the transport boundary conditions that were developed for that research.

Publications

D. Dundas, Journal of Chemical Physics,136 194303 (2012)

Staff involved

Daniel Dundas
Jim McCann