COMPARING 90K DATA TO SOLID STATE AB-INITIO CALCULATIONS FROM CRYSTAL92 Anthony Martin, Dept of Chemistry, University of Toledo, Toledo, OH 43606, USA. A. Alan Pinkerton, Dept of Chemistry, University of Toledo, Toledo, OH 43606,USA, A. Barry Kunz, Dept of Electrical Engineering, Michigan Technological University, Houghton, MI 49931, USA.

Accurate X-ray diffraction measurements on Ammonium Dinitramide, Biguanidinium Dinitramide and bis-Biguanidinium Dinitramide have been made at 90K. The resulting multipole refinements are compared to the calculated charge densities at the 6-21G basis set level using CRYSTAL92 for each system. The solid state ab-initio calculations use the 90K unit cell and geometries. The N-H bonds are all fixed at idealised neutron positions. Thus, there is no geometry optimiztion in the ab-initio calculation. The ab-initio calculations are all at 0K and do not include any zero-point energy. Thermal motion has been taken into account by either setting the multipole thermal parameters to zero before calculating charge densities from the x-ray data or thermally smearing the ab-initio data with the experimental thermal parameters.

Preliminary work indicates that there are significant differences in the position of the bonds and lone pair peaks when the two methods are compared.