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Manuscript Title: Small angle scattering data analysis for dense polydisperse systems: the FLAC program.
Authors: F. Carsughi, A. Giacometti, D. Gazzillo
Program title: FLAC
Catalogue identifier: ADNF_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 133(2000)66
Programming language: Fortran.
Computer: Digital Workstation AU 433, Pentium I MMX 200 MHz, Macintosh Powerbook G3 400 MHz.
Operating system: Digital UNIX 4.0E, Windows NT service pack 4, MacOS 9.0.2.
RAM: 640K words
Word size: 32
Keywords: Small-angle scattering, Hard spheres, Polydispersity, Percus-Yevick, Mean spherical approximation, Solid state physics, Neutron.
Classification: 7.6.

Nature of problem:
The problem is the calculation of the scattering cross section in small-angle scattering of polydisperse neutral and charged hard spheres. Both dense or dilute systems are considered.

Solution method:
The algorithms implemented here are obtained by solving the Orstein-Zernike integral equations within the Percus-Yevick and mean spherical approximation closures for neutral and charged hard spheres, respectively [1,2].

Only hard sphere (neutral or charged) potentials are used.

Unusual features:
Routines of the Harwell Subroutine Library (HSL) are included. Their use must be acknowledged in any paper publishing results obtained by FLAC. The entire code must be linked with the International Mathematical Statistical Libraries (IMSL).

Running time:
A test run considers 200 points for defining the size distribution function and calculates the scattering cross section over 2^13 points, without any smearing effects. For neutral hard spheres, on a Digital Workstation AU 433 this test takes 7.7 s, while on the Macintosh and on the PC 26.1 and 49.6 s, respectively. On including instrumental smearing considering only one experimental configuration (by convoluting over 11 points) the CPU time on the Digital Workstation AU 433 increases up to 46.8 s; if multiple scattering correction is also taken into account (by using 2^7 points for the 2D Fourier transform), the CPU time is 47.3 s. Furthermore, the addition of a vertical slit (sampled by 2^6 points) requires 270.1 s of CPU time. For charged hard spheres, the calculation without any correction takes 12.1 s of CPU time.

[1] A. Vrij, J. Chem. Phys. 69 (1978) 1742; 71 (1979) 3267.
[2] D. Gazzillo, A. Giacometti, F. Carsughi, J. Chem. Phys. 107 (1997) 10141.