This is a feasibility study of a possible influence of anharmonic thermal motion of hydrogen atom(s) on quantitative electron density distributions in single crystals of model compounds. The direct aim of this project is to model the anharmonic motion of hydrogen atoms for compounds containing only small number of H-atoms (in the range from 1 to 3) by using high resolution variable temperature single crystal elastic neutron scattering data. The critical information obtained from the model of motion of the H -atom will then be used in the complementary high resolution X-ray charge density studies performed at the same temperatures. Thus, we will verify the influence of anharmonic thermal motion of H-atoms on other structural and electronic parameters such as, for example, the electron density distributions at the X-H covalent bonds and X-H¿Acceptor hydrogen bonding.