Elsepa—Dirac partial-wave calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules (New Version Announcement)

Abstract

A new version of the Fortran program elsepa, which calculates differential and integrated cross sections for elastic scattering of electrons and positrons, is presented. Details of the program and its applications are given in the original paper [Comput. Phys. Commun.165 (2005) 157–190]. Dirac phase shifts are now calculated by using the recently published subroutine package radial (Salvat and Fernández-Varea, 2019), which solves the radial wave equation for real or complex central potentials by means of a robust and accurate power-series method. In addition, elastic collisions with atoms in elemental solids are described by using the muffin-tin optical model potential proposed by Bote et al., (2009), which is somewhat more elaborate and flexible than that in the original elsepa code and allows adjusting the absorption potential to give inelastic cross sections in close agreement with empirical data. With the use of the radial subroutines, the work of elsepa is reduced to (1) the definition of the interaction potential and (2) the summation of the partial-wave series of the scattering amplitudes. The structure of the new code has been simplified and stricter criteria for the convergence of the partial-wave series have been adopted. The distribution package includes gnuplot scripts for easy visualization of the calculation results. Program summaryProgram Title:elsepaCPC Library link to program files:https://doi.org/10.17632/w4hm5vymym.1Licensing provisions: CC BY NC 3.0Programming language: Fortran 90Journal reference of previous version: Comput. Phys. Commun. 165 (2005) 157–190Does the new version supersede the previous version?: YesReasons for the new version: This new version offers increased accuracy, and a more flexible modeling of elastic collisions of electrons and positrons with atoms in elemental solids.Summary of revisions: The calculation of phase shifts is now performed by the generic subroutines of the radial package [1]. A more flexible optical-model potential for scattering in solids is included [2]. Stricter criteria for convergence of the partial-wave series are applied. The distribution package has been reorganized, with the numerical database files now placed in a separate directory; scripts for direct visualization of the calculation results with the plotting program gnuplot (http://www.gnuplot.info) are also included.Nature of problem: The code calculates differential cross sections, total cross sections and transport cross sections for single elastic scattering of electrons and positrons by neutral atoms, positive ions and randomly oriented molecules. When the energy of the projectile is less than about 5 MeV, the programs also compute scattering amplitudes and spin polarization functions.Solution method: The effective interaction between the projectile and the target atom is represented by a local central potential that can optionally include an imaginary (absorptive) part to account approximately for the coupling with inelastic channels. For projectiles with kinetic energy less that about 5 MeV, the code performs a conventional relativistic Dirac partial-wave analysis. For higher kinetic energies, where the convergence of the partial-wave series is too slow, approximate factorization methods are used. The programs only admit kinetic energies higher than 5 eV, a practical lower limit that may be changed by editing the source files.Additional comments including restrictions and unusual features: The calculations are based on the static-field approximation. The optional correlation-polarization and inelastic absorption corrections are obtained from approximate, semi-empirical models. elsepa allows considering an absorption potential only for projectiles with energies less than about 1 MeV; for higher energies, the absorption potential is set to zero to prevent the occurrence of numerical instabilities. Calculations for molecules are based on a single-scattering independent-atom approximation. To ensure accuracy of the results for scattering by ions, the electron density of the ion must be supplied by the user; it can be generated, e.g., by running the program dhfs of the radial package [1].AcknowledgmentsWe are indebted to Dr John Villarrubia for pointing out various cases of incomplete convergence of the original code. Financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades / Agencia Estatal de Investigación, Spain / European Regional Development Fund , European Union, (project no. RTI2018-098117-B-C22) is gratefully aknowledged.