Polymorphism is a common feature of many molecular materials The "Holy Grail" would be the ability to predict the appearance of polymorphism in a particular molecular system, and predict the solid structures adopted. With this in view we propose to examine polymorphic systems using the experimental QTAIM charge density approach, to provide detailed information about the intermolecular interactions. The fundamental data for these studies are high resolution X-ray diffraction data, obtained from both laboratory and synchrotron sources. However the treatment of the H atoms is often crucial in obtaining a proper deconvolution of thermal motion from charge density effects. It is therefore highly desirable to obtain direct experimental evidence for the anisotropic thermal motion. We propose to obtain single crystal neutron data from SXD on two polymorphs of sulfathiazole and cabamazepine.