We present an application of pseudopotentials to ab initio calculations of elastic and electronically inelastic electron-molecule-collision cross sections. 'We use the Schwinger multichannel method (SMC) implemented with the local-density norm-conserving pseudopotentials of Bachelet, Hammann, and Schliiter [Phys. Rev. B 26, 4199 (1982)]. In our procedure, the core electrons and protons are replaced by the nonlocal but single-particle pseudopotential and the valence electrons are treated in a many-body framework, as in the SMC method. Our calculated integral and differential cross sections are in very good agreement with previous all-electron calculations, PACS number(s): 34.80.Bm, 34.80.Gs

Measured and calculated differential cross sections for elastic ͑rotationally unresolved͒ electron scattering from two primary alcohols, methanol ͑CH 3 OH͒ and ethanol ͑C 2 H 5 OH͒, are reported. The measurements are obtained using the relative flow method with helium as the standard gas and a thin aperture as the collimating target gas source. The relative flow method is applied without the restriction imposed by the relative flow pressure conditions on helium and the unknown gas. The experimental data were taken at incident electron energies of 1, 2, 5, 10, 15, 20, 30, 50, and 100 eV and for scattering angles of 5°-130°. There are no previous reports of experimental electron scattering differential cross sections for CH 3 OH and C 2 H 5 OH in the literature. The calculated differential cross sections are obtained using two different implementations of the Schwinger multichannel method, one that takes all electrons into account and is adapted for parallel computers, and another that uses pseudopotentials and considers only the valence electrons. Comparison between theory and experiment shows that theory is able to describe low-energy electron scattering from these polyatomic targets quite well.

In this paper, we report integral and differential cross sections for the electronic excitation of H 2 molecules by electron-impact. Our scattering amplitudes were calculated using the Schwinger multichannel method within the minimal orbital basis for single configuration interactions (MOB-SCI) level of approximation. Through the use of the present strategy we have investigated the coupling effects among ground state and first singlet and triplet states of the same spatial symmetry. The five-state (nine for degenerated states) close-coupling calculations joined the advantages of a well-described set of physical states of interest with a minimum associated pseudo-state space. The results obtained by means of the MOB-SCI technique show a significant improvement towards experimental data in comparison with previous two-channel close-coupling calculations.

We present a formulation for low-energy positron-molecule collisions based on the Schwinger multichannel method (SMC) which was previously adapted for electron-molecule scattering. We have preserved very important features of the SMC such as its ability to deal with electronically inelastic scattering and its applicability to molecular targets of arbitrary geometry. Our implementation also allows for the inclusion of a substantial number of closed electronic channels to represent polarization effects, which are very important at low impact energies. As an application, to illustrate the form with which polarization is represented in this formulation, we have calculated elastic integral and differential cross sections for e+-H2 and e+-CH4 collisions. We included all possible single-particle excitations from the target and found substantial disagreement with respect to model potential calculations and attenuated-beam experimental data. We discuss possible reasons for these discrepancies.

We discuss some recent developments in the implementation of the Schwinger multichannel method for electron-molecule collision calculations. The evaluation of matrix elements involving the operator VGp+'V, previously accomplished by insertion of a Gaussian basis on either side of Gz+', is now done by direct numerical quadrature. This approach avoids the necessity of very large Gaussian basis sets, allowing the size of the basis to reAect only the dynamical requirements of the scattering wave function. We 6nd that the reduction in the required basis size results in improved efBciency, in spite of the additional numerical efFort of performing the quadrature. Trial applications to electron-CH4 scattering in the static-exchange approximation and to electronic excitation of H2 illustrate the excellent convergence characteristics of the procedure.