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.

Abstract. The Schwinger multichannel method [K. V. McKoy, Phys. Rev. A 30, 1734 (1984)], which is based on the Schwinger variational principle for the scattering amplitude [J. Schwinger, Phys. Rev. 72, 742 (1947)], was designed to account for exchange, polarization and electronically multichannel coupling effects in the low-energy region of electron scattering from molecules with arbitrary geometry. The applications of the method became more ambitious with the availability of computer power combined with parallel processing, use of norm-conserving pseudopotentials and improvement of the description of target excited states (minimal orbital basis for single configuration interaction). The most recent applications involving 33 and 45 electronically open channels for phenol and ethylene molecules, represent good examples of the present status of the method. In this colloquium, we review the strategy and point out new directions to apply the method in its full extension.

We report normalized experimental and theoretical differential cross sections for elastic electron scattering by C 4 H 4 O (furan) molecules from a collaborative project between several Brazilian theoretical groups and an experimental group at California State Fullerton, USA. The measurements are obtained by using the relative flow method with helium as the standard gas and a thin aperture target gas collimating source. The relative flow method is applied without the restriction imposed by the relative flow pressure condition on helium and the unknown gas. The experimental data were taken at incident electron energies of 1, 1.5, 1.73, 2, 2.7, 3, 5, 7, 10, 20, 30, and 50 eV and covered the angular range between 10 • and 130 • . The measurements verify observed π * shape resonances at 1.65 ± 0.05eV and 3.10 ± 0.05 eV scattering energies, in good agreement with the transmission electron data of Modelli and Burrow [J. Phys. Chem. A 108, 5721 (2004)]. Furthermore, the present results also indicated both resonances dominantly in the d-wave channel. The differential cross sections are integrated in the standard way to obtain integral elastic cross sections and momentum transfer cross sections. The calculations employed the Schwinger multichannel method with pseudopotentials and were performed in the static-exchange and in the static-exchange plus polarization approximations. The calculated integral and momentum transfer cross sections clearly revealed the presence of two shape resonances located at 1.95 and 3.56 eV and ascribed to the B 1 and A 2 symmetries of the C 2v point group, respectively, in very good agreement with the experimental findings. Overall agreement between theory and experiment regarding the differential, momentum transfer, and integral cross sections is very good, especially for energies below 10 eV.

We report on the shape resonance spectra of uracil, 5-fluorouracil, and 5-chlorouracil, as obtained from fixed-nuclei elastic scattering calculations performed with the Schwinger multichannel method with pseudopotentials. Our results are in good agreement with the available electron transmission spectroscopy data, and support the existence of three π∗ resonances in uracil and 5-fluorouracil. As expected, the anion states are more stable in the substituted molecules than in uracil. Since the stabilization is stronger in 5-chlorouracil, the lowest π∗ resonance in this system becomes a bound anion state. The present results also support the existence of a low-lying σCCl (*) shape resonance in 5-chlorouracil. Exploratory calculations performed at selected C-Cl bond lengths suggest that the σCCl (*) resonance could couple to the two lowest π∗ states, giving rise to a very rich dissociation dynamics. These facts would be compatible with the complex branching of the dissociative electron attachment cross sections, even though we cannot discuss any details of the vibration dynamics based only on the present fixed-nuclei results.