I gather that the wk1995 and it1992 scattering tables come from Waasmaier & Kirfe (1995), Acta Cryst. A51, 416-431 and the International Tables Vol C 1992 respectively.

Can someone please tell me from where the n_gaussian scattering tables are derived?

Hi Aaron, this is the default option for X-ray form-factors used in Phenix that is dynamically optimized for best possible speed and accuracy given atomic model and diffraction data, described here Grosse-Kunstleve, R. W., Sauter, N. K. & Adams, P. D. (2004). IUCr Comput. Comm. Newsl. 3, 22–31. http://www.phenix-online.org/papers/iucrcompcomm_jan2004.pdf Pavel