Abstract
We report on density functional calculations (DFT) of elastic integral scattering cross-sections for positron collisions with argon, krypton, nitrogen and methane. The long-range asymptotic polarization potential is described using higher-order terms going much beyond an induced dipole potential (−α / r 4) while the short-range interaction is modeled by two different forms of electron – positron correlation potential (Boronski-Nieminen and Quantum Monte Carlo potentials). The results of both approaches agree quite well with the recent theoretical and measured values. Based on the present and previous theoretical and experimental data we discuss some systematics observed in integral scattering cross-sections below the positronium formation threshold. In particular we point out on the correlation between the values of scattering cross-sections and atomic dimensions.
Highlights
“An exact determination of actual atomic dimensions” is the problem that was already posed by A
A detailed analysis of the influence of the magnetic field on the angular resolution was developed; allowing making appropriate corrections in the low-energy region, see for example [14]. This allows to evidence three regions in the low energy positron total cross sections for atomic and some non-polar molecular targets: a very low energy range where the TCS rises in the zeroenergy limit, a rather flat dependence up to the positronium threshold, and at higher energies a rise due to the positronium formation [16,17]
At collision energies below 0.5 eV the cross sections computed with the BN-functional are about 50 percent higher than those obtained with the Quantum Monte Carlo (QMC)-functional
Summary
“An exact determination of actual atomic dimensions” is the problem that was already posed by A. Low-energy (below 1 eV) experiments by Ramsauer [4] showed deep minima in cross sections for Ar, Kr, Xe and CH4 This triggered the quantum wave mechanics, but hindered trials to derive atomic dimensions via electron scattering. A detailed analysis of the influence of the magnetic field on the angular resolution was developed; allowing making appropriate corrections in the low-energy region, see for example [14] This allows to evidence three regions in the low energy positron total cross sections for atomic and some non-polar molecular targets: a very low energy (below 1 eV) range where the TCS rises in the zeroenergy limit, a rather flat dependence up to the positronium threshold, and at higher energies a rise due to the positronium formation [16,17]. In the twocomponent density functional theory [23] it plays a similar role as the exchange-correlation potential in Kohn-Sham theory [24]
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