A Complete Computational Approach to Atomic Collisions

Significant Achievements, Anticipated Outcomes and Future Work

The results of our atomic collision modelling on the APAC National Facility during 2003 have been extraordinarily successful and have greatly exceeded our expectations. We have extended the method of exterior complex scaling (ECS) to incorporate a highly efficient propagating/iterative algorithm, which has generated the most accurate calculations undertaken to date for electron-hydrogen ionising collisions. We were also able to generate these results with a one-hundred-fold reduction in supercomputing resources over previous ECS implementations. This very significant breakthrough has allowed us to apply the ECS method to collisions over a wider range of energies, and a wider range of targets, which was thought to be unachievable with existing supercomputing technology. We are presently undertaking a detailed examination of ionising collisions at very low energies. In 2004/2005 we will extend the ECS method to collisions with multi-electron atoms, which will require a dramatic increase in supercomputing resources, but only possible through the computational efficiency of our method.

Computational Techniques Used

The computer software used on the APAC National Facility has been developed specifically for this project using FORTRAN and the OpenMP multiprocessor directives. The bulk of the computational effort is devoted to performing matrix inversions using the LAPACK linear algebra library. However, as our method involves the manipulation of both sparse and dense arrays, both real and complex, a large number of the linear algebra operations have been custom written, as no standard library routines were available to calculate them efficiently.

With the extension of our ECS technique to multi-electron atoms in the coming year, our computer software will be modified to use SCALAPACK and incorporate the MPI multiprocessor subroutines, so that it can utilise multiple computing nodes concurrently. The success of this extension is dependant upon the high speed network switch of the APAC National Facility SC, which will allow very high speed internode data transfer, and the availability of a large number of processors. As our method is very memory intensive, more 8 gigabyte nodes and the ability to schedule multi-node jobs to these 8 gigabyte nodes (and access all their memory) will be a distinct advantage.

Publications, Awards and External Funding

External Funding and Awards

None

Publications

P. L. Bartlett, A. T. Stelbovics, Exterior complex scaling method applied to differential ionization cross sections of hydrogenic targets Z <= 4, Phys. Rev. A, In press, 2004.
P. L. Bartlett, A. T. Stelbovics, A complete direct method for electron-hydrogen scattering: Application to the collinear and Temkin-Poet models, Phys. Rev. A, In press, 2004.
A. T. Stelbovics, P. L. Bartlett, I. Bray, A. S. Kadyrov, Three-body Coulomb Scattering above the Ionization Threshold, Physica Scripta, In press, 2004.
P. L. Bartlett, A. T. Stelbovics, I. Bray, Propagating exterior complex scaling method for electron-hydrogen collisions, J. Phys. B, 37, 2004, L69-L76.
P. L. Bartlett, A. T. Stelbovics, Electron-impact ionization cross sections for elements Z=1 to Z=54, At. Data Nucl. Data Tab., In Press, 2003.
P. L. Bartlett, I. Bray, S. Jones, A. T. Stelbovics, A. S. Kadyrov, K. Bartschat, G. L. Ver Steeg, M. P. Scott, P. G. Burke, Unambiguous ionization amplitudes for electron-hydrogen scattering, Phys. Rev. A, 69, 2003, 020702(R).
P. L. Bartlett, A. T. Stelbovics, I. Bray, Threshold ionization laws for electron-hydrogen scattering and their dominant region of configuration space, Phys. Rev. A, 69, 2003, 030701(R).
P. L. Bartlett, A. T. Stelbovics, Born total ionisation cross sections: An algebraic computing program using Maple, Comp. Phys. Comm., 154, 2003, 159-174.