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Manuscript Title: A program for the calculation of the intensities of X-ray or neutron powder reflections, Part 3.
Authors: I.F. Ferguson, A.D. Hardy, M.U. Modi, A.H. Rogerson
Catalogue identifier: ACFX_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 32(1984)83
Programming language: Fortran.
Computer: ICL 2982.
Operating system: VME/B.
RAM: 1951K words
Word size: 8
Peripherals: magnetic tape.
Keywords: Crystallography, Intensities, X-ray, Neutron, Powder diffraction, Structure factor, Crystal structure, Dispersion correction, Unit cell, Symmetry.
Classification: 8.

Subprograms used:
Cat Id Title Reference
AAQB_v1_0 FIREFLY II CPC 5(1973)328
AAQB_v2_0 FIREFLY IV CPC 10(1975)42

Nature of problem:
The program FIREFLY VI (FIRECOMET) is an extension of the earlier programs FIREFLY II and IV. It calculates the intensities of X-ray or neutron Bragg reflections with particular reference to the powder method. The program is very flexible and allows the intensities of some or all the reflections to be calculated provided the unit cell and its contents are specified together with the equipment used and, if necessary, temperature and absorption factors. Provision is made for the comparison of observed and calculated data, the calculation of an R factor, the input of fractional co-ordinates, and the input of atomic co-ordinates which refer only to the asymmetric unit. The program can apply a dispersion correction to the calculated intensities. Unlike FIREFLY IV, it is no longer necessary to input the Miller indices of each reflection in order to compute the entire X-ray powder pattern, for the program can derive these from the given unit cell.

Solution method:
The Bragg reflection intensities are calculated by the standard formulae of X-ray and neutron diffraction as applied to powder diffraction.

The program is written to manipulate up to 999 sets of Miller indices, 2000 atoms with co-ordinates xn, yn, and zn, and no more than 400 atom types, 10 wavelengths and 999 observed intensities and Bragg angles (theta values).

Running time:
30 s.