Introduction

EPolyScat is a suite of FORTRAN 90 programs and libraries that can be used to study electron-molecule scattering processes. This includes both scattering of electrons from neutral and ionic molecules and molecular photoionization. The current version of the codes only treats single electronic states using a several different optical potentials to represent the interaction between the electron and the molecule. The primary potential is the static-exchange correlation-polarization (SECP) potential. The program can also treat positron-molecule scattering using a selection of model local potentials.

The codes have been developed as a collaboration of the groups of Lucchese and Gianturco beginning in 1993. The primary references for the development of the numerical methods used are given below in the bibliography.

A given calculation uses a series of independent programs that exchange information through formatted text files. The full calculation can then be obtained through an appropriate c-shell script that runs all the required programs. To assist in the construction of the appropriate run script there is a script SetUp.com which creates scratch directories and defines a number of commands through the alias mechanism of the c-shell. These commands then invoke the various programs with the appropriate input variables. To transfer data to the programs, there is a single data file which contains labeled data records that are then read by the programs and commands as needed. There are also commands to add and delete data from the data file. In order to run correctly, there are a few c-shell environment variables which must also be defined. Finally, there are a number of sample jobs which illustrate how the EPolyScat suite can be run.


Program directories

In the root directory of the EPolyScat programs are the following subdirectors:

com
contains script files that define commands, compile programs, transfer the programs over the network, and make the HTML manual.
dat
contains some precalculated b_(lm)s (for Td, Oh, Ih).
src
contains fortran source files.
tests
contains standard tests.

Terms

The following terms are are used repeatedly in the pages of this manual and are defined for the purposes of these programs as follows:

b_(lm)
the expansion coefficients of the symmetry adapted harmonics in the basis set of the real harmonics. These are described in detail in S. L. Altmann, "On the symmetries of spherical harmonics," Proc. Cambridge Phil. Soc. 53 (Part 2), 343-367 (1957).
Component of an IR
the basis function of the irreducible representation, This is represented by an integer.
Data file
this is a file (fixed to be fort.95) that contains a series of data records that are used to control the calculation and to pass data from one program to the next.
Data record
a single group of data that are given a symbolic label. The format is described in detail in the description of the AddData command. These recodrs are processed using unformatted FORTRAN reads.
Initial state
in a photoionization calculation, the initial state is the unionized bound state.
IR
irreducible representation, for each point group the various IRs are represented by either an integer or a five character string.
Multiread data record
a data record that is read using more than one unformatted FORTRAN read statements and thus must be represented by more than one line in the data file.
Orbital group
consists of the a set of degenerate molecular orbitals. If an orbital is nondegenerate then its orbital group just contains one orbital. For degenerate orbitals, the number of orbitals in the group is the dimension of the IR which the orbitals transform as. The members of the group are then indexed the the same manner as the components of the IR. All of the input in the program are in terms of orbital groups. For example, one specifies the number of orbital groups and the occupations of each orbital group.
Spin degeneracy
an integer that gives the spin degeneracy of a particular state, i.e. 1 for a singlet, 2 for a doublet, etc.
Symmetry type
the full specification of the symmetry of an object including the IR it transforms as and the component of that IR. This is represented as either a character string (LEN = 7) or and an integer which indexes the IR and component in a single list containing all IRs and their components.
Target state
the bound state that the electron scatters from. In a photoionization calculation of a neutral molecule, this is the ionized state after the photoelectron has left the system.
Total scattering state
the combined scattering state including the target state and the continuum electron.

Bibliography

  1. F. A. Gianturco, R. R. Lucchese, N. Sanna, and A. Talamo, A Generalized Single Center Approach for Treating Electron Scattering from Polyatomic Molecules, in Electron Collisions with Molecules, Clusters, and Surfaces, edited by H. Ehrhardt and L. A. Morgan, (Plenum, New York, 1994) pp. 71-86.
  2. F. A. Gianturco, R. R. Lucchese, and N. Sanna, On the Scattering of Low-Energy Electrons by Sulphur Hexafluoride, J. Chem. Phys. 102, 5743-5751 (1995).
  3. Robert R. Lucchese and F. A. Gianturco, One-Electron Resonances in Electron Scattering from Polyatomic Molecules, Intern. Rev. Phys. Chem. 15, 429-466 (1996).
  4. F. A. Gianturco and Robert R. Lucchese, One-Electron Resonances and Computed Cross Sections in Electron Scattering from the Benzene Molecule, J. Chem. Phys. 108, 6144-6159 (1998).
  5. F. A. Gianturco, R. R. Lucchese, and N. Sanna, Computed elastic cross sections and angular distributions of low-energy electron scattering from gas phase C60 fullerene, J. Phys. B 32, 2181-2193 (1999).
  6. Alexandra P. P. Natalense and Robert R. Lucchese, Cross section and asymmetry parameter calculation for sulfur 1s photoionization of SF6, J. Chem. Phys. 111, 5344-5348 (1999); Erratum, J. Chem. Phys. 112, 501 (2000).
  7. F. A. Gianturco and Robert R. Lucchese, One-particle resonances in low-energy electron scattering from C60, J. Chem. Phys. 111, 6769-6786 (1999).
  8. F. A. Gianturco and Robert R. Lucchese, A computational investigation of positron scattering from C60, Phys. Rev. A 60, 4567-4576 (1999).
  9. F. A. Gianturco and R. R. Lucchese, Electron scattering from gaseous SF6: Comparing calculations with experiments, J. Chem. Phys. 114, 3429-3439 (2001).