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Positron-atom interactions studied using configuration interaction methods

Bromley, Michael William James (2002). Positron-atom interactions studied using configuration interaction methods. PhD Thesis, Northern Territory University.

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Author Bromley, Michael William James
Title Positron-atom interactions studied using configuration interaction methods
Institution Northern Territory University
Publication Date 2002
Thesis Type PhD
Subjects 0299 - Other Physical Sciences
Abstract The non-relativistic configuration interaction (CI) method is applied to the study of positron interactions with either one or two valence electron atoms possessing a positron-atom bound state. Although the binding energy and other atomic properties are slowly convergent with respect to the angular momenta of the single particle orbitals used to construct the CI wavefunctions, the calculations are sufficiently large to give usefully accurate descriptions of the positronic atom structures. Calculations of the accurately known positron-atom bound states; positronic copper (e+Cu), positronic lithium (e+Li), and positronium hydride (PsH) systems were undertaken to develop and refine the numerical procedures. CI calculations confirmed the stability of three other systems; positronic beryllium (e+Be), positronic magnesium (e+Mg), and positronic zinc (e+zn). The e+Mg calculations independently resolves the disagreement between the University of New South Wales group and a previous computational approach of the Northern Territory University group. Further CI calculations demonstrated the stability of four systems; positronic calcium (e+Ca), copper positride (CuPs), positronic strontium (e+Sr) and positronic cadmium (e+Cd). These predictions are all rigorous with respect to the underlying model Hamiltonians. CI convergence issues are examined in detail, with trends used to give estimated binding energies (in units of Hartree) of 0.037795 (PsH), 0.000886 (e+Li), 0.003083 (e+Be), 0.016151 (e+Mg), 0.016500 (e+Ca), 0.005088 (e+Cu), 0.014327 (CuPs), 0.003731 (e+zn), 0.010050 (e+Sr) and 0.006100 (e+Cd). The CI program used for the structure calculations was adapted to perform scattering calculations via the imposition of plane-wave boundary conditions within the Kohn variational formalism. Test calculations of model potential and low-energy elastic positron-hydrogen scattering reveal that in practice, the effects of 'Schwartz' singularities are insignificant. CI-Kohn calculations of low-energy (k = 0 → 0.2 a0-1 ) elastic positron-copper scattering gave a scattering length of +13.7 ao and a threshold Zeff of 69.3, explicitly demonstrating that Zeff is not overly large for such a metal vapour. These investigations demonstrate the feasibility of using single particle orbitals centred on the nucleus to reliably describe certain classes of positronic systems with one or two valence electrons.


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