Analysis of experimental X-ray scattering from almost spherical molecules: Estimates of the influence of the force , where is the exchange-correlation potential of DFT for and

The X-ray scattering factor from a spherical electron density is first written in terms of an integrated quantity Q(r) which is defined as the number of electrons inside a sphere of radius r centred at the origin. It is emphasized that Q ( r ) e 2 / r 2 , having dimensions of force, involves from density functional theory a term - ∂ V xc / ∂ r , where V xc is the exchange-correlation potential. The role that this potential plays in affecting the X-ray scattering from NH 4 + and CH 4 is thereby estimated semiquantitatively. Future work to obtain fully quantitative numerical results for CH 4 is finally proposed.