FPRIME

2.5 - FPRIME - Calculation of Dispersion Factors

The program FPRIME supplies the real and imaginary dispersion terms for any wavelength, as well as the photon interaction cross-section (in barns/atom ). These are necessary for SHELXL when using X-radiation other than Mo, Cu or Ag (e.g. from synchrotron sources). The user should select the wavelength used (in Angstroms) and then the chemical elements in the structure under consideration.

The program writes SHELX format dispersion cards to the file DISP.OUT. These should be pasted in the model .INS file immediately AFTER the SFAC card and BEFORE the UNIT card. Since all the other scattering factor terms are independent of radiation wavelength, it is only necessary to include these DISP cards as well as the normal SFAC card. This procedure is carried out automatically by Initialise Files if WinGX detects an unusual wavelength, (i.e. not MoKalpha, CuKalpha or AgKalpha).

FPRIME is a Windows implementation of the FPRIME code written by Don Cromer and revised by Bob von Dreele at the Los Alamos Laboratory. The Jensen term is not used, and the corrections to f' tabulated by Kissel and Pratt (Acta Cryst (1990), A46, 170) are applied.