Relativistic X-ray elastic scattering factors for neutral atoms Z=1-54 from multi-configuration Dirac-Fock wavefunctions in the 0-12 angstrom(-1) sin theta/lambda range, and six-Gaussian analytical expressions in the 0-6 angstrom(-1) range

X-ray elastic scattering factors for the ground-state atoms H to Xe have been calculated from the relativistic wavefunctions in the 0-12 Angstrom(-1) sin theta/lambda range and fitted in the 0-6 Angstrom(-1) sin theta/lambda range to a sum of six Gaussian functions for three different sin theta/lambda ranges. More than one configuration was included for elements with several electronic configurations having the same subshell occupancy. The resulting parameterized scattering factors are significantly more accurate than those previously published. Separate core-and valence-electron scattering values have also been obtained. The relativistic atomic energies, the atomic second moments and the limiting values of the electron scattering factor as sin theta/lambda approaches zero have been tabulated. The wavefunctions were calculated with the GRASP92 program package [Parpia, Froese Fischer & Grant (1996). Comput. Phys. Commun. 94, 249-271] with the optimal level (OL) model rather than with the extended average level (EAL) model used in previous calculations [Rez, Rez & Grant (1994). Acta Cryst. A50, 481-497].