Multiconfigurational two-centre convergent close-coupling approach to positron scattering on helium

Abstract

The convergent close-coupling method with two-centre expansions has been developed to calculate positron scattering on helium. The method utilizes a multiconfigurational description of helium wavefunctions. Positronium formation is taken into account explicitly as electron capture into the positronium states. Direct-scattering, positronium-formation and breakup cross sections are calculated at all energies of practical relevance. Convergence in the calculated cross sections is demonstrated by increasing the basis size and orbital quantum number of the included states for each of the centres. Better agreement with experimental data is found when a multiconfigurational description is used for the helium wavefunctions in comparison with the recent frozen-core results.

Low-energy positron interactions with krypton

“…One is the relativistic optical potential (ROP) calculation [23], which has been used to calculate the grand total cross section σ GT below E Ps and the grand total minus Ps formation (σ GT -σ Ps ) above E Ps . The other approach is the convergent close-coupling (CCC) approach [24] and is a calculation of σ GT at all energies. Both techniques have been discussed in detail recently [18], and only a brief description is given here.…”

“…In this region the presence of the Ps formation channel, leading also to ionization, requires a two-center expansion for accurate calculations. This problem has now been solved by new CCC formulations for helium [24], and work is currently ongoing to extend the two-center technique to the heavier noble gases. Good agreement between the present experimental results and the earlier theoretical results of Baluja and Jain [1] is noted above 30 eV.…”

Convergent close coupling calculations for positron-magnesium scattering

“…Currently we are approaching the positron-magnesium scattering problem using the two-centre CCC method that has recently been developed and extensively tested for positron-helium scattering by Utamuratov et al [3].…”

A Self-Consistent Model for Positronium Formation from Helium Atoms

“…Consequently, the total cross sections obtained from the two formalisms converge at high energies. Figure 2 compares the total positronium-formation cross sections obtained from our formalism with the experimental measurements of Diana et al [28], Fromme et al [29], Fornari et al [30], Overton et al [31] and Murtagh et al [32] and also with the results of the CBA with Z T = 1.6875, 2 and √ −2ǫ i [52] and of the two-center convergent close-coupling (CCC) formalism [18]. As Fig.…”

“…This has motivated numerous studies of collisions in which electrons in atomic or molecular targets are captured by positrons [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. In a collision, each of the various modes into which the system under study may be fragmented is called a channel.…”