Stopping powers of antiprotons in H, He, Ne, Ar, Kr, and Xe targets are calculated using a semiclassical time-dependent convergent close coupling method. The helium target is treated using both frozen-core and multiconfiguration approximations. The electron-electron correlation of the target is fully accounted for in both cases. Double ionization and ionization with excitation channels are taken into account using an independent-event model. The Ne, Ar, Kr and Xe atom wave functions are described in a model of six p-shell electrons above a frozen Hartree-Fock core with only one-electron excitations from the outer p-shell allowed. Results obtained for helium in the multiconfiguration treatment are in better agreement with experimental measurements than other theories.

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A fully quantal integral-equation approach to ion-atom collisions is developed along the lines of the convergent close-coupling approach to electron-atom scattering. The approach starts from the exact three-body Schrödinger equation for the scattering wavefunction and leads to coupled-channel Lippmann-Schwinger equations for the transition amplitudes in the impact-parameter representation, with the relative motion of the heavy particles treated quantum mechanically. The method is applied to calculate antiproton collisions with atomic hydrogen. Integrated total, excitation and ionization cross sections are calculated in the energy range from 1 keV to 1 MeV.

A general single-centre close-coupling approach based on a continuum-discretisation procedure is developed to calculate excitation and ionization processes in ion-atom collisions. The continuous spectrum of the target is discretised using stationary wave packets constructed from the Coulomb wave functions, the eigenstates of the target Hamiltonian. Such continuum discretisation allows one to generate pseudostates with arbitrary energies and distribution. These features are ideal for detailed differential ionization studies. The approach starts from the semiclassical three-body Schrödinger equation for the scattering wave function and leads to a set of coupled differential equations for the transition probability amplitudes. To demonstrate its utility the method is applied to calculate collisions of antiprotons with atomic hydrogen. A comprehensive set of benchmark results from integrated to fully differential cross sections for antiproton-impact ionization of hydrogen in the energy range from 1 keV to 1 MeV is provided. Contrary to previous predictions, we find that at low incident energies the singly differential cross section has a maximum away from the zero emission energy. This feature could not be seen without a fine discretisation of the low-energy part of the continuum.

Details of the recently developed quantum-mechanical two-center convergent close-coupling approach (Abdurakhmanov et al 2016 J. Phys. B: At. Mol. Phys. 49 03LT01) to proton-hydrogen scattering are presented. The formulation is based on the exact (fully quantum-mechanical) three-body Schrödinger equation. The total scattering wavefunction is expanded using a two-center pseudostate basis. This allows one to include all underlying processes, namely, direct scattering and ionization, electron capture into bound and continuum states of the projectile. The off-shell integration in the coupled-channel Lippmann–Schwinger integral equations emerging from the three-body Schrödinger equation for the scattering wavefunction is taken analytically which greatly reduces computational effort. While the calculated electron capture cross sections are in a good agreement with experiment, some discrepancy exists for the ionization cross sections.

Stopping powers of antiprotons in H2 and H2O targets are calculated using a semiclassical timedependent convergent close-coupling method. In our approach the H2 target is treated using a twocenter molecular multiconfiguration approximation, which fully accounts for the electron-electron correlation. Double ionization and dissociative ionization channels are taken into account using an independent-event model. The vibrational excitation and nuclear scattering contributions are also included. The H2O target is treated using a neonization method proposed by Montanari and Miraglia [J. Phys. B 47 015201 (2014)], whereby the ten-electron water molecule is described as a dressed Ne-like atom in a pseudo-spherical potential. Despite being the most comprehensive approach to date, the results obtained for H2 only qualitatively agree with the available experimental measurements.

Wavepacket continuum-discretisation approach is used to calculate excitation, ionization and electron-capture (ec) cross sections for proton collisions with n=2 states of atomic hydrogen, where n is the principal quantum number. The approach assumes a classical motion for the projectile and is based on the solution of the three-body Schrödinger equation using the two-center expansion of the total scattering wave function. The scattering wave function is expanded in an orthonormal basis set built from negative-energy eigenstates and wavepacket pseudostates representing the continuum of both the target atom and the atom formed by the projectile after capturing the electron. With a sufficiently large basis, due to the strong coupling between channels, the method produces converged cross sections for direct-scattering, ionization and ec processes simultaneously. For the quasi-elastic transitions, where both orbital and magnetic quantum numbers change, the integrated cross section is infinite. Nevertheless, the corresponding transitions probabilities are finite at any given impact parameter, indicating that the angular differential cross sections can be measured. Calculated cross sections for scattering on the metastable 2s state are compared with other theoretical results obtained using atomic-orbital close-coupling and classicaltrajectory Monte Carlo approaches. Considerable disagreement with previous calculations has been found for some transitions at various incident energies.

A recently developed fully quantal convergent-close-coupling (CCC) approach (Abdurakhmanov et al 2011 J. Phys. B: At. Mol. Opt. Phys. 44 075204) to ion-atom collisions is extended to differential ionization studies. An important feature of the method is that it does not have classical limitations on the relative motion of participating particles. The approach is applied to calculate fully differential, as well as various doubly and singly differential cross sections of ionization in antiproton collisions with atomic hydrogen. The CCC results for various differential cross sections agree reasonably well with the results of the semiclassical CC and the continuum-distorted-wave-eikonal-initial-state approaches, particularly at high energies. However, some discrepancies exist at low energies, where the final state interactions among colliding particles are found to be very important.