Model-potential approach to positron elastic scattering from noble gases

Positron-electron correlation-polarization potentials for the calculation of positron collisions with atoms and molecules*

“…For the long-range part of the polarization potential we include a number of terms of higher order. The importance of higher-order polarization terms in positron-atom scattering calculations has been shown previously by Gianturco and De Fazio [31], Gianturco et al [32], and by Poveda et al [33].…”

A rigid sphere approach to positron elastic scattering by noble gases, molecular hydrogen, nitrogen and methane

“…In real scattering the repulsive potential is not so steep as the rectangular wall, the polarization potential needs some "cut-off" modifications [10,12,22] and at the intermediate distances (some 1 − 3a 0 ) a sharp matching from our model is "smoothedout" by the short-range correlation potential (see Fig. 1 where the present potential is compared with other, more realistic models).…”

“…For example, many-body theory [19] requires an inclusion of virtual positronium, convergent-close-coupling formalism takes into account coupling effects to virtual positronium formation channels [20], whereas polarized-orbital [13][14][15][16][17][18], DFT [10,12] and model-potential [21,22] approaches need higher multipole terms (quadrupole, octupole, hyperpolarizability) in long-range polarization in order to get good agreement with experiments. The present results show that the lack of attractive virtual effects, short-range correlations and higher long-range multipoles can be effectively compensated by very deep minimum of dipole polarization potential (for example −α/2R 4 0 ≈ −49 eV for Ar, see Fig.…”

“…For positrons the repulsive static potential is counterbalanced solely by an attractive polarization potential making computational approaches very sensitive to the short-range positron -target's electrons (nonadiabatic) correlations. High quality (but computationally expensive) models have been developed to challenge this problem including, for example, approximate density functional theory (DFT) by Gianturco et al [12], polarizedorbital calculations by McEachran and Stauffer [13] and McEachran et al [14][15][16][17][18], many-body theory with virtual positronium formation by Green et al [19], convergent close-coupling (CCC) method by Fursa and Bray [20] and semi-empirical potential model for ab initio calculations by Assafrão et al [21] and Poveda et al [22]. All these approaches were able to successfully reproduce shapes and magnitudes of experimental elastic scattering cross-sections for most noble gases, though they are not fully consistent, particularly in the prediction of scattering lengths.…”

“…The latter is found to be compatible with the position of principal maximum in the radial distribution of outermost orbital (defined here as the atomic radius) for atomic targets. Providing the present model we benefit also from the fact that the de Broglie wavelength of positron with kinetic energy below the positronium formation threshold is usually comparable or much greater than the di- [22] and Franz et al [10] are also presented.…”