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A new computational framework for molecular dynamics

Final Report Summary - HPCAMO (A new computational framework for molecular dynamics.)

The advent of new light sources (NLS) with extreme characteristics (compared with those of conventional laser light) opened up a new scientific territory. Free-Electron Laser (FEL) sources, delivering tunable and intense radiation in the VUV and XUV regimes, produce light capable of interacting directly with the inner-shell electrons of matter. On the other hand the development of really short duration light pulses (durations on the sub-femtosecond time-scale) allows the exploration and control of the dynamics of physical processes occurring in the interiors of atoms and molecules.

The main aim of this project was to develop a theoretical and computational framework capable of describing the dynamics of a multielectron molecular system exposed to strong and/or ultra-short duration laser. We focused on a new time-dependent theoretical developments of R-matrix theory which, in a time-independent form, has already been applied over many years to complex atomic and molecular systems.

More specifically, the main project objectives were (a) The development of a theoretical and computational framework for the handling of ionization dissociation channels of molecules in a strong radiation field. (b) The development of an ab initio time-dependent theory presently for the description of the interaction of the hydrogen molecule ion generally with intense light and (c) developing a high-performance computational code.

In light of the extreme computational demands for a realistic description of the processes involved, we explored numerical and computational innovations to suit the problem at hand. We have ended to the use of a recently emerged computational paradigm based on the uniqure capabilities of the graphics processor units (GPUs). We have implemented a code on a Graphics Processor Unit (GPU) using a freely available parallel library, namely the openCL. This was a hard task and to the best of our knowledge we are among the first to implement such a code in solving the time-dependent Schrodinger equation of atomic/molecular systems in intense laser fields. The above developed code and the application of it in the molecular hydrogen ion for a particular process has resulted to two publications and one under consideration.
One of the objective was also to develop further the present methodology and apply to other systems as well as for example in atomic systems.

An important social-economic impact of the present project was that we have been able to develop and demonstrate the use of relatively new computational paradigm. The use of GPUs represents an alternative way of supercomputing low-cost platform, which is ideally suited to medium-size institutes that can't afford expensive super-computing systems.

Finally, such a theoretical and computational framework has enabled us to cope with a large class of problems of experimental and theoretical interest in view of the latest breakthroughs in LASER and FEL technology. In terms of radiation characteristics the applicability of the theory ranges from the far infrared (fraction of eV) to the soft X-ray (keV) spectral band and pulse durations from attoseconds to hundreds of femtoseconds.

1. Role of broadband-laser-pulse temporal extent in H2+ photodissociation Phys. Rev. A 86, 043428 – Published 24 October 2012, E. P. Benis, M. Bakarezos, N. A. Papadogiannis, M. Tatarakis, S. Divanis, C. Ó Broin, and L. A. A. Nikolopoulos

2. An OpenCL implementation for the solution of the time-dependent Schrödinger equation on GPUs and CPUs Original Research Article
Computer Physics Communications, Volume 183, Issue 10, October 2012, Pages 2071-2080
Cathal Ó Broin, L.A.A. Nikolopoulos

3. Submitted for publication to Computer Physics Communications 'A GPGPU based program to solve the TDSE in intense laser fields through the finite difference approach.', Cathal O'Broin and L.A.A Nikolopoulos