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Manuscript Title: Differential cross sections for electron/positron scattering from polyatomic molecules.
Authors: N. Sanna, F.A. Gianturco
Program title: POLYDCS
Catalogue identifier: ADJB_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 114(1998)142
Programming language: Fortran.
Computer: IBM RS/6000.
Operating system: AIX 4.X, DU 4.Ox Linux RedHat 4.2.
Word size: 64
Keywords: Electron/positron Molecule, Scattering, Differential cross, Sections, Polar targets, Molecular physics.
Classification: 16.5.

Nature of problem:
Scattering of slow electrons and positrons from polyatomic molecules of arbitrary shape. Elastic angular distributions and rotationally inelastic differential cross sections.

Solution method:
The body-fixed (BF) K-matrices [1] describing the electron/positron-molecule collision at a given energy are read in from an external file and transformed into the Space Fixed (SF) frame of reference. The SF K-matrices are then used to calculate state-to-state rotationally elastic and inelastic cross sections by summing the AL [2] coefficients as a Legendre polynomial expansion [3]. Linear, spherical, symmetric and asymmetric rotors are evaluated with the inclusion of the Born correction [4] for polar molecular targets.

Depending on the molecular target (number of partial waves in the BF K-matrices) and on the required solution (angular resolution) the problem may or may not fit into available RAM memory since, for the sake of performance, all the runtime relevant quantities are stored on non-volatile RAM instead of on disk.

Unusual features:
The code has been engineered to use global parameters with thresholds suitable to run typical jobs for small-medium size molecular targets. Under some unusual circumstances, using a larger set of those parameters may cause the program to run with unexpected performance reductions due to runtime bottlenecks like memory swap which strongly depend on the hardware used. Furthermore, the present code provides the only generally available code to obtain rotationally inelastic angular distributions form electron (positron) scattering from non linear polyatomic targets.

Running time:
The execution time strongly depends on the molecular target description and on the hardware/OS chosen; it must be pointed out that an absolute scaling law of the CPU requirement is at present undeterminable. Typically, the job running time may vary from a few seconds to a couple of hours on a DEC Alpha ev56 @ 400 MHz depending on the runtime parameters.

[1] N. Sanna, R.R. Lucchese and F.A. Gianturco, POLYSCAT, Comp. Phys. Commun. (in preparation).
[2] F.A. Gianturco and A. Jain, Phys. Rep. 143 (1986) 347.
[3] A. Jain and D.G. Thompson, Comp. Phys. Commun. 32 (1984) 367.
[4] D. Norcross and N.T. Padial, Phys. Rev. A 25 (1981) 226.