The recent production of atoms of antihydrogen as well as advances in particle trap and beam technologies have generated considerable interest in the interaction of antiparticles with regular matter and with each other. Though it is tempting to think of a positron as just a "positive electron" in terms of its interaction with atoms and molecules, there are significant differences that are most apparent at low and intermediate energies. One of the most interesting phenomena in the field of positron collisions with matter---and one that has no electron-scattering counterpart---is the formation of real and virtual positronium (Ps) and the manner in which this charge-exchange process affects the elastic scattering. There is also keen interest in making and trapping "exotic" systems, such as antihydrogen and positronium hydride, for use in basic research, and potentially, as an extremely compact energy storage mechanism.

The goal of the current research is to modify and extend existing quantum chemistry technologies so that accurate interaction potential surfaces can be used to compute integrated total and differential cross sections (DCS) for a variety of positron-atom and positron-molecule systems. Some of the distinguishing features of this research include:

• The use of concurrent computers and algorithms to extend what is "computationally practical."
• A new treatment of short-range correlation between the positron and the electrons of the target.
• Downloadable results for positron collisions with various target atoms and molecules.

The Paper Chase

1. Paper: J. Franz , F. A. Gianturco, K. L. Baluja, J. Tennyson, R. Carey, R. Montuoro, R. R. Lucchese, T. Stoecklin, P. Nichols, T. L. Gibson, "Correlation-Polarization Effects In Electron/Positron Scattering From Acetylene: A Comparison Of Computational Models," Nucl. Instrum. Methods Phys. Res. B 266, 425-434 (2008). [Link].
2. Paper: F.A. Gianturco, P. Nichols, T.L. Gibson, and R.R. Lucchese, "Metastable Trapping of Low-Energy Positrons by Cubane: A Computational Experiment," Phys. Rev. A 72, 032724 (2005). [Link].
3. Paper: F.A. Gianturco, T.L. Gibson, P. Nichols, R.R. Lucchese, and T. Nishimura, "Modelling Dynamical Correlation Forces In Low-Energy Positron Scattering From Polyatomic Gases: A Comparison for CH4," Radiat. Phys. Chem. 68, 673-680 (2003). [Link]. Preprint: [pdf] (217 KB).
4. Book Chapter: Robert R. Lucchese, F. A. Gianturco, P. Nichols, and Thomas L. Gibson, "A Test Calculation on SF6 of Model Potentials for Correlation and Polarization Effects in Positron Scattering from Molecules," Chapter 25 in New Directions in Antimatter Physics and Chemistry, edited by Clifford M. Surko and Franco A. Gianturco (Kluwer Academic, Dordrecht, 2001). Preprint: [gzipped ps] (494 KB); [zipped ps] (494 KB); [pdf] (700 KB).
5. Paper: Thomas L. Gibson, "Low-Energy Positron-H₂ Collisions in the Distributed Positron Model," J. Phys. B 25, 1321-1336 (1992). [Link].
6. Paper: Thomas L. Gibson, "A Modified Adiabatic Approach to Positron-Atom and Positron-Molecule Polarization Potentials: Application to Positron-He Scattering," J. Phys. B 23, 767-776 (1990). [Link].
7. Paper: Brian K. Elza, Thomas L. Gibson, Michael A. Morrison, and Bidhan C. Saha, "Non-Adiabaticity and Other Aspects of Polarisation in Positron-Molecule Scattering," J. Phys. B 22, 113-130 (1989). [Link].
8. Paper: Michael A. Morrison, Thomas L. Gibson, and David Austin, "Polarization Potentials for Positron-Molecule Collisions: Positron-H₂ Scattering," J. Phys. B 17, 2725-2745 (1984). [Link].

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