Complementary aspects of charge and momentum density for the study of the chemical bond

Charge density can be accessed through accurate X-ray diffraction by crysta ls. It has recently become a rather routine technique. Refinement models en able a fair description of charge density changes due to chemical bonding a nd cohesive forces. Conversely, momentum density is observable through inco herent Compton scattering, in particular by use of high-intensity synchrotr on sources. We present results concerning a first attempt at a simultaneous refinement of a model wavefunction on both diffraction and Compton data, f or MgO and LiH crystals. It is shown that if the diffraction data are highl y sensitive to local effects and their symmetry around atomic sites. Compto n data are very dependent on the delocalization processes of electrons. Mor eover. Compton measurements show a systematic deviation from self-consisten t-held model calculations and this is analyzed in terms of an empirical cor relation model for anions in insulators. Possible future extensions of such studies are finally discussed.